1.
2.
3.
4.
5.
Which of the following is (are) important in determining whether a reaction occurs?
I.
Energy of the molecules
II.
Orientation of the molecules
A.
I only
B.
II only
C.
Both I and II
D.
Neither I nor II
Consider the reaction between solid CaCO3 and aqueous HCl. The reaction will be speeded up by an increase
in which of the following conditions?
I.
Concentration of the HCl
II.
Size of the CaCO3 particles
III.
Temperature
A.
I only
B.
I and III only
C.
II and III only
D.
I, II and III
The reaction between NO2 and F2 gives the following rate data at a certain temperature.
What is the order of reaction with respect to NO2 and F2?
[NO2]/mol dm–3
[F2]/mol dm–3
0.1
0.2
0.1
0.2
0.2
0.4
0.1
0.4
0.2
NO2 order
F2 order
A.
first
first
B.
first
second
C.
second
first
D.
second
second
Rate /mol dm–3
min–1
Which step in a multi-step reaction is the rate determining step?
A.
The first step
B.
C.
The step with the lowest activation energy D.
The last step
The step with the highest activation energy
Excess magnesium was added to a beaker of aqueous hydrochloric acid on a balance. A graph of the mass of
the beaker and contents was plotted against time (line 1).
Mass
1
2
Time
1
What change in the experiment could give line 2?
A.
6.
7.
I.
The same mass of magnesium but in smaller pieces
II.
The same volume of a more concentrated solution of hydrochloric acid
III.
A lower temperature
I only
B.
II only
C.
III only
D.
None of the above
The rate of a reaction between two gases increases when the temperature is increased and a catalyst is added.
Which statements are both correct for the effect of these changes on the reaction?
Increasing the temperature
Adding a catalyst
A.
Collision frequency increases
Activation energy increases
B.
Activation energy increases
Activation energy does not change
C.
Activation energy does not change
Activation energy decreases
D.
Activation energy increases
Collision frequency increases
The rate expression for a reaction is shown below.
rate = k[A]2[B]2
Which statements are correct for this reaction?
A.
8.
II.
The overall order of the reaction is 4.
III.
Doubling the concentration of A would have the same effect on the rate of reaction as doubling the
concentration of B.
I and II only
B.
I and III only C.
II and III only
D.
I, II and III
I.
The size of the molecules
II.
The distance between the molecules
III.
The average kinetic energy of the molecules
I only
B.
II only
C.
III only
D.
I and II only
Based on the definition for rate of reaction, which units are used for a rate?
A.
10.
The reaction is second order with respect to both A and B.
Which of the following is (are) altered when a liquid at its boiling point is converted to a gas at the same
temperature?
A.
9.
I.
mol dm–3
B. mol time–1 C. dm time–1
D.
mol dm–3 time–1
Which of the quantities in the enthalpy level diagram below is (are) affected by the use of a catalyst?
Enthalpy
I
II
III
Time
2
A.
11.
I only
k versus T
14.
C.
I and II only
D.
II and III only
B.
k versus 1
T
C.
ln k versus T
D.
ln k versus 1
T
In the Haber process for the synthesis of ammonia, what effects does the catalyst have?
A.
B.
C.
D.
13.
III only
Values of a rate constant, k, and absolute temperature, T, can be used to determine the activation energy of a
reaction by a graphical method. Which graph produces a straight line?
A.
12.
B.
Rate of formation of NH3(g)
Increases
Increases
Increases
No change
Amount of NH3(g) formed
Increases
Decreases
No change
Increases
Which step is included in the definition of the term rate determining step?
A.
the step with the slowest moving particles B.
the step with the fewest reactant particles
C.
the slowest step in a reaction
the last step in a reaction
D.
The rate expression for a particular reaction is
Rate = k[P][Q]
Which of the units below is a possible unit for k?
A.
15.
16.
17.
18.
mol–2 dm6 min–1
B. mol–1 dm3 min–1 C. mol dm3 min–1
D. mol–2 dm–6 min–1
Which statement is correct about the behaviour of a catalyst in a reversible reaction?
A.
It decreases the enthalpy change of the forward reaction.
B.
It increases the enthalpy change of the reverse reaction.
C.
It decreases the activation energy of the forward reaction.
D.
It increases the activation energy of the reverse reaction.
Which statement is correct for a collision between reactant particles leading to a reaction?
A.
Colliding particles must have different energy.
B.
All reactant particles must have the same energy.
C.
Colliding particles must have a kinetic energy higher than the activation energy.
D.
Colliding particles must have the same velocity.
Which change of condition will decrease the rate of the reaction between excess zinc granules and dilute
hydrochloric acid?
A.
increasing the amount of zinc
B.
increasing the concentration of the acid
C.
pulverize the zinc granules into powder
D.
decreasing the temperature
The reaction 2X(g) + Y(g)  3Z(g) has the rate expression
rate = k [X]2[Y]0
3
The concentration of X is increased by a factor of three and the concentration of Y is increased by a factor of
two. By what factor will the reaction rate increase?
A.
19.
6
B. 9
C. 12
D.18
The table shows the concentrations of reactants and products during this reaction.
2A + B  C + 2D
[A] / mol dm–3
[B] / mol dm–3
[C] / mol dm–3
[D] / mol dm–3
at the start
6
3
0
0
after 1 min
4
2
1
2
The rate of reaction can be measured by reference to any reactant or product. Which rates are correct for this
reaction?
I.
II.
III.
A.
20.
rate = –2 mol dm–3 min–1 for A
rate = –1 mol dm–3 min–1 for B
rate = –1 mol dm–3 min–1 for C
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
A reaction occurs in four steps. The steps and their rates are shown in the table
Step
Rate
1
0.01 mol dm–3 s–1
2
0.10 mol dm–3 s–1
3
0.01 mol dm–3 min–1
4
0.10 mol dm–3 min–1
Which is the rate-determining step?
21.
A.
Step 1
B.
Step 2
C.
Step 3
D.
Step 4
The rate expression for a reaction is
rate = k[CH3Br][OH–]
Which is a possible unit for k?
22.
A.
mol2 dm–6 min–1
B.
mol dm–3 min–1
C.
mol–1 dm3 min–1
D.
mol–2 dm6 min–1
What happens to the rate constant (k) and activation energy (Ea) of a reaction when the temperature is
4
increased?
23.
24.
A.
k increases and Ea is unaffected.
B.
k decreases and Ea is unaffected.
C.
Ea increases and k is unaffected.
D.
Ea decreases and k is unaffected.
Some reactions occur in a series of steps. Which is the best description of the rate-determining step in a
reaction mechanism?
A.
The step involving the greatest number of reactant particles
B.
The step involving the smallest number of reactant particles
C.
The step releasing the most energy
D.
The step with the highest activation energy
The mechanism of a reaction is
XY2 + XY2  X2Y4
X2Y4  X2 + 2Y2
X2 + Y2  2XY
What is the overall equation for the reaction?
25.
26.
A.
X2Y4  2XY2
B.
2XY2  X2 + 2Y2
C.
2XY2  2XY + Y2
D.
X2Y4  2XY + Y2
In general, the rate of a reaction can be increased by all of the following except
A.
increasing the temperature.
B.
increasing the activation energy.
C.
increasing the concentration of reactants.
D.
increasing the surface area of the reactants.
At 25C, 100 cm3 of 1.0 mol dm–3 hydrochloric acid is added to 3.5 g of magnesium carbonate. If the sample
of magnesium carbonate is kept constant, which conditions will not increase the initial rate of reaction?
Volume of HCl / cm3
Concentration of HCl / mol dm–3
Temperature / C
A.
200
1.0
25
B.
100
2.0
25
C.
100
1.0
35
D.
200
2.0
25
5
27.
28.
At 25C, 100 cm3 of 1.0 mol dm–3 hydrochloric acid is added to 3.5 g of magnesium carbonate. If the sample
of magnesium carbonate is kept constant, which conditions will not increase the initial rate of reaction?
Volume of HCl / cm3
Concentration of HCl / mol dm–3
Temperature / C
A.
200
1.0
25
B.
100
2.0
25
C.
100
1.0
35
D.
200
2.0
25
Consider the reaction
2I(aq) + H2O2(aq) + 2H+(aq)  I2(aq) + 2H2O(l)
In the presence of S2O32–(aq) and starch solution, the time taken for a blue colour to form was observed at
various reactant concentrations.
Experiment
[I–] / mol dm–3
[H2O2] / mol dm–3
[H+] / mol dm–3
Time / s
1
0.10
0.12
0.01
25
2
0.05
0.12
0.01
50
3
0.10
0.06
0.01
100
What is the correct order with respect to I– and H2O2?
29.
30.
I–
H2O2
A.
1
2
B.
1
2
1
4
C.
2
1
D.
2
4
Which statement is correct with regard to the catalysed and uncatalysed pathways for a given reaction?
A.
The enthalpy change of the catalysed reaction is less than the enthalpy change for the uncatalysed
reaction.
B.
The enthalpy change of the catalysed reaction is greater than the enthalpy change for the uncatalysed
reaction.
C.
The enthalpy change of the catalysed reaction is equal to the enthalpy change for the uncatalysed
reaction.
D.
The activation energy of the catalysed reaction is greater than the activation energy for the uncatalysed
reaction.
Which statement is correct about the rate expression for a chemical reaction?
A.
It can be determined from its chemical equation.
B.
It can be predicted from the value of ΔHӨ for the reaction.
C.
It can be calculated from the effect of temperature on the reaction.
D.
It can be determined by measuring the change in concentration of a reactant or product over time.
6
31.
32.
Which changes increase the rate of a chemical reaction?
I.
Increase in the concentration of an aqueous solution
II.
Increase in particle size of the same mass of a solid reactant
III.
Increase in the temperature of the reaction mixture
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
For the reaction 2NO2(g) + F2(g)  2NO2F(g) the accepted mechanism is
NO2(g) + F2(g)  NO2F(g) + F(g)
NO2(g) + F(g)  NO2F(g)
slow
fast
What is the rate expression for this reaction?
33.
34.
A.
rate = k[NO2]2[F2]
B.
rate = k[NO2][F2]
C.
rate = k[NO2][F]
D.
rate = k[NO2]2
The activation energy, of a reaction can be obtained from the rate constant, k, and the absolute temperature, T.
Which graph of these quantities produces a straight line?
A.
k against T
B.
k against
C.
ln k against T
D.
ln k against
1
T
1
T
Excess magnesium, was added to a beaker of aqueous hydrochloric acid. A graph of the mass of the beaker and
contents was plotted against time (line 1).
Mass
1
2
Time
What change in the experiment could give line 2?
A.
The same mass of magnesium in smaller pieces
7
35.
B.
The same volume of a more concentrated solution of hydrochloric acid
C.
A lower temperature
D.
A more accurate instrument to measure the time
Which quantities in the enthalpy level diagram are altered by the use of a catalyst?
I
Enthalpy
II
III
Time
36.
37.
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
What is the order of reaction with respect to NO2(g) and F2(g) given the following rate data at a certain
temperature?
[NO2(g)] / mol dm–3
[F2(g)] / mol dm–3
Rate / mol dm–3 min–1
0.1
0.2
0.1
0.2
0.2
0.4
0.1
0.4
0.2
Order with respect to NO2(g)
Order with respect to F2(g)
A.
first
first
B.
first
second
C.
second
first
D.
second
second
(i)
Draw a graph to show the distribution of energies in a sample of gas molecules. Label the axes and label
your curve T1. Using the same axes, draw a second curve to represent the distribution of energies at a
higher temperature. Label this curve T2.
(3)
(ii)
State and explain, with reference to your graph, what happens to the rate of a reaction when the
temperature is increased.
…………………………………………………………………………………………..
8
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
(2)
(Total 5 marks)
38.
The data below refer to a reaction between X and Y.
Initial concentration /
mol dm–3
(i)
Initial rate of reaction /
mol dm–3 s–1
Experiment
X
Y
1
0.25
0.25
1.0×10–2
2
0.50
0.25
4.0×10–2
3
0.50
0.50
8.0×10–2
Define the term order of reaction.
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
(1)
(ii)
Deduce the order of reaction with respect to both X and Y. Explain your reasoning.
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
(4)
(iii)
Write the rate expression for the reaction and calculate the rate constant, including its units.
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
9
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
(4)
(iv)
Calculate the initial rate of reaction when the initial concentrations of X and Y are 0.40 mol dm–3 and
0.60 mol dm–3 respectively.
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
(2)
(Total 11 marks)
39.
The graph below shows the volume of carbon dioxide gas produced against time when excess calcium
carbonate is added to x cm3 of 2.0 mol dm–3 hydrochloric acid.
Volume of CO 2
Time
(i)
Write a balanced equation for the reaction.
…………………………………………………………………………………………..
…………………………………………………………………………………………..
(1)
(ii)
State and explain the change in the rate of reaction with time. Outline how you would determine the rate
of the reaction at a particular time.
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
10
…………………………………………………………………………………………..
…………………………………………………………………………………………..
(4)
(iii)
Sketch the above graph on an answer sheet. On the same graph, draw the curves you would expect if:
I.
the same volume (x cm3) of 1.0 mol dm–3 HCl is used.
II.
double the volume (2x cm3) of 1.0 mol dm–3 HCl is used.
Label the curves and explain your answer in each case.
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
(5)
(Total 10 marks)
40.
The reaction between 2-bromo-2-methylpropane (CH3)3CBr, and warm aqueous 0.100 mol dm–3 sodium
hydroxide solution to form 2-methylpropan-2-ol, is found to have the following rate expression.
rate =k[(CH3)3CBr]
(i)
State what is meant by the term rate of reaction.
…………………………………………………………………………………………..
…………………………………………………………………………………………..
(1)
(ii)
State the units for the rate constant, k.
…………………………………………………………………………………………..
…………………………………………………………………………………………..
(1)
(iii) Deduce what the effect on the rate of the reaction will be if the concentration of the sodium hydroxide
solution is increased to 0.300 mol dm–3.
…………………………………………………………………………………………..
…………………………………………………………………………………………..
(1)
(iv) Deduce the overall order of the reaction.
…………………………………………………………………………………………..
(1)
(v)
It is found that after 32.0 seconds the concentration of 2-bromo-2-methylpropane falls to
value. Calculate the half-life for the reaction.
1
16
of its initial
…………………………………………………………………………………………..
11
…………………………………………………………………………………………..
(1)
(Total 5 marks)
41.
When excess lumps of magnesium carbonate are added to dilute hydrochloric acid the following reaction takes
place.
MgCO3(s) + 2HCl(aq) → MgCl2(aq) + CO2(g) + H2O(l)
(a)
Outline two ways in which the rate of this reaction could be studied. In each case sketch a graph to show
how the value of the chosen variable would change with time.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(4)
(b)
State and explain three ways in which the rate of this reaction could be increased.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
12
(6)
(c)
State and explain whether the total volume of carbon dioxide gas produced would increase, decrease or
stay the same if
(i)
more lumps of magnesium carbonate were used.
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
(2)
(ii)
the experiments were carried out at a higher temperature.
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
(2)
(Total 14 marks)
42. Carbon dioxide gas in the atmosphere reacts slightly with rainwater as shown below.
CO2(g) + H2O(l)
(i)
State the meaning of the
H+(aq) + HCO3–(aq)
sign.
……………………………………………………………………………………………
(1)
(ii)
Predict the effect, if any, of the presence of a catalyst on the acidity of rainwater. Give a reason for your
answer.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(2)
(iii)
Use Le Chatelier’s principle to predict the effect of the addition of a small quantity of an alkali on the
acidity of rainwater. Explain what effect, if any, this would have on the equilibrium constant, Kc.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(3)
(Total 6 marks)
13
43.
Oxygen and nitrogen monoxide react together to form nitrogen dioxide.
O2(g) + 2NO(g) → 2NO2(g)
The graph below shows how the initial rate of reaction changed during an experiment in which the initial
[NO(g)] was kept constant whilst the initial [O2(g)] was varied.
Rate
[O 2 (g)]
(a)
Deduce, giving a reason, the order of reaction with respect to O2
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(2)
(b)
In a series of experiments, the initial [O2(g)] was kept constant while the initial [NO(g)] was varied. The
results showed that the reaction was second order with respect to NO. Sketch a graph to show how the
rate of reaction would change if the initial
[NO(g)] was increased.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(2)
(c)
Deduce the overall order of this reaction.
……………………………………………………………………………………………
……………………………………………………………………………………………
(1)
(d)
State and explain what would happen to the initial rate of reaction if the initial concentration of NO was
doubled and that of O2 was halved.
14
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(3)
(e)
When the initial values are [O2(g)] = 1.0×10–2 mol dm–3 and [NO(g)] = 3.0×10–2 mol dm–3, the initial
rate of reaction is 6.3×10–4 mol dm–3s–1. Write the rate expression for this reaction and calculate the rate
constant, stating its units.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(4)
44.
The compound iodine chloride, ICl, reacts with hydrogen to form iodine and hydrogen chloride.
(i)
Deduce the equation for this reaction.
(1)
(ii)
The kinetics of this reaction were studied at a certain temperature, when all the reactants and products
were in the gas phase. The table shows the initial rate of reaction for different concentrations of
reactants.
Experiment
[ICl] / mol dm–3
[H2] / mol dm–3
Initial rate /
mol dm–3 s–1
1
0.100
0.0500
5.00×10–3
2
0.200
0.0500
1.00×10–2
3
0.200
0.0250
2.50×10–3
Deduce and explain the order of reaction with respect to ICl and to H2.
(4)
(iii)
Write the rate expression for the reaction.
(1)
(iv)
Use information from Experiment 1 to determine the value, with units, of the rate constant for the
reaction.
(2)
(v)
Determine the rate of reaction when the concentrations of reactants in Experiment 1 are both doubled.
(1)
(Total 9 marks)
45.
(a)
The variation of the rate constant, k, for a reaction with temperature is shown by the Arrhenius equation.
Two versions of this equation are shown in Table 1 of the Data Booklet.
(i)
Explain the significance of the Arrhenius constant, A, in this equation.
(1)
15
(ii)
Explain what is meant by the term activation energy,Ea.
(1)
(iii)
Describe how, using a graphical method, values of A and Ea can be obtained for a reaction.
(5)
(b)
The equation for a reaction used in industry is
CH2CH2 + Cl2  CH2ClCH2CL HӨ = –185 kJ
Iron(III) chloride can be used as a catalyst for the reaction.
(i)
Explain the difference between the terms homogeneous and heterogeneous when applied to a
catalyst.
(1)
(ii)
Draw an enthalpy level diagram for this reaction, including labels for HӨ, Ea and the activation
energy when a catalyst is used, Ecat.
(4)
46.
Excess 0.100 mol dm–3 nitric acid is added to a certain mass of powdered calcium carbonate at 20C. The rate
of reaction is monitored by measuring the change in mass over time due to the loss of carbon dioxide.
2HNO 3 ( aq) + Ca CO3 (s)→ C a ( NO 3) 2 (aq) + H 2O (l) + CO 2 (g)
Mass loss / g
Time / minutes
(a)
Define the term rate of reaction.
....................................................................................................................................
....................................................................................................................................
(1)
(b) Explain why the mass loss remains constant after a certain time.
....................................................................................................................................
....................................................................................................................................
(1)
(c)
Draw a line on the graph above, to show what the graph would look like if the same mass of calcium
carbonate in larger pieces were reacted with excess 0.100 mol dm–3 nitric acid.
(1)
16
(d)
Explain in terms of the collision theory what would happen to the rate if the reaction was conducted at
50C.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
(e)
Determine the rate of formation of carbon dioxide when the nitric acid reacts at a rate of 2.0010–3 mol
cm–3 s–1.
....................................................................................................................................
....................................................................................................................................
47.
Nitrogen(II) oxide reacts with bromine according to the following equation.
2NO(g) + Br2(g)  2NOBr(g)
H = negative
The data below were obtained for the reaction between NO(g) and Br2(g) at a specified temperature and
pressure.
(a)
Experiment
Initial [NO] /
mol dm–3
Initial [Br2] /
mol dm–3
Initial rate / mol dm–3 s–1
1
2.00×10–2
5.00×10–3
3.20×10–3
2
2.00×10–2
2.50×10–3
1.60×10–3
3
4.00×10–2
5.00×10–3
1.30×10–2
Determine, giving a reason, the order of reaction with respect to NO and the order of reaction with
respect to Br2.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(b) Derive the rate expression for the reaction between NO and Br2.
....................................................................................................................................
17
....................................................................................................................................
(1)
(c)
Calculate the rate constant for the rate expression using experiment 1 and state its units.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(d) If the total volume of the reaction mixture was doubled at constant temperature, state the effect, if any,
on
(i)
the rate constant.
.........................................................................................................................
.........................................................................................................................
(1)
(ii)
the rate of change of the Br2(g) concentration.
.........................................................................................................................
.........................................................................................................................
(1)
(e)
Draw a labelled enthalpy level diagram for the reaction between NO(g) and Br2(g), with and without the
use of a catalyst.
(3)
(Total 10 marks)
48.
(i)
Draw a graph that shows the distribution of molecular energies in a sample of a gas at two different
temperatures, T1 and T2, such that T2 is greater than T1.
(2)
(ii)
Define the term activation energy.
(1)
(iii)
State and explain the effect of a catalyst on the rate of an endothermic reaction.
(2)
(Total 5 marks)
49. (i)
Magnesium is added to a solution of hydrochloric acid. Sketch a graph of acid concentration on the
y-axis against time on the x-axis to illustrate the progress of the reaction.
(1)
(ii)
Describe how the slope of the line changes with time.
(1)
(iii)
Use the collision theory to state and explain the effect of decreasing concentration on the rate of the
reaction.
18
(2)
50.
(i)
The reaction between propanone, CH3COCH3 and bromine, Br2 in the presence of acid, H+, is found to
be second order overall, but the rate is independent of the bromine concentration. Write three possible
rate expressions for the reaction.
(3)
(ii)
The concentration of each of the three reactants was doubled in three separate experiments. Choose one
of the rate expressions in (i) and predict the effect on the rate of the reaction of each of these changes.
(2)
(iii)
The graph below shows how the concentration of propanone changes with time in a reaction.
1.8
1.6
1.4
1.2
1.0
Concentration
/ mol dm–1
0.8
0.6
0.4
0.2
0.0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
Time / s
Use the graph to confirm that the reaction is first order with respect to propanone showing your working.
(2)
(iv) The overall reaction is:

 CH3COCH2Br(aq) + HBr(aq)
CH3COCH3(aq) + Br2(aq) H(aq)
Describe one observation that would allow you to follow the progress of the reaction. State and explain
the role of the acid in the reaction.
(4)
(Total 11 marks)
51.
The compounds with the molecular formula C4H9Br all undergo nucleophilic substitution reactions when
warmed with sodium hydroxide solution. The equation for each of the reactions is
C4H9Br + OH–  C4H9OH + Br–
When the reaction of one of these compounds was investigated the following kinetic data were obtained.
Experiment number
1
2
3
Initial [C4H9Br]
/mol dm–3
0.010
0.020
0.020
Initial [OH–]
/mol dm–3
0.010
0.010
0.020
Initial rate of reaction
/mol dm–3 min–1
2.0×10–3
4.0×10–3
4.0×10–3
19
(a)
Explain the term nucleophilic substitution.
……………………………………………………………………………………….
……………………………………………………………………………………….
……………………………………………………………………………………….
(2)
(b) Deduce the order of reaction with respect to C4H9Br.
……………………………………………………………………………………….
(1)
(c)
Deduce the order of reaction with respect to OH– and explain your answer.
……………………………………………………………………………………….
……………………………………………………………………………………….
……………………………………………………………………………………….
……………………………………………………………………………………….
(2)
(d)
State the rate expression for the reaction.
……………………………………………………………………………………….
(1)
(e)
Calculate the value of the rate constant for the reaction and state its units.
……………………………………………………………………………………….
……………………………………………………………………………………….
……………………………………………………………………………………….
……………………………………………………………………………………….
(2)
(f)
Give the equations for the mechanism of this reaction.
(2)
(g)
Define the term rate-determining step and identify this step in the mechanism.
……………………………………………………………………………………….
……………………………………………………………………………………….
……………………………………………………………………………………….
(2)
20
(h)
Define the term molecularity and deduce its value in the mechanism.
……………………………………………………………………………………….
……………………………………………………………………………………….
……………………………………………………………………………………….
(2)
(Total 14 marks)
21
52.
The reaction between ammonium chloride and sodium nitrite in aqueous solution can be represented by the
following equation.
NH4Cl(aq) + NaNO2(aq) → N2(g) + 2H2O(l) + NaCl(aq)
The graph below shows the volume of nitrogen gas produced at 30 second intervals from a mixture of
ammonium chloride and sodium nitrite in aqueous solution at 20°C.
140
120
100
Volume of N 2 / cm 3
80
60
40
20
0
0
20 40 60 80 100 120 140 160 180
Time / s
(a)
(i)
State how the rate of formation of nitrogen changes with time. Explain your answer in terms of
collision theory.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
(2)
(ii)
Explain why the volume eventually remains constant.
............................................................................................................................
............................................................................................................................
(1)
(b) (i)
State how the rate of formation of nitrogen would change if the temperature were increased from
20°C to 40°C.
............................................................................................................................
............................................................................................................................
(1)
(ii) State two reasons for the change described in (b)(i) and explain which of the two is more
important in causing the change.
............................................................................................................................
22
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
(3)
(iii)
The reaction between solid ammonium chloride and aqueous sodium nitrite can be represented by
the following equation.
NH4Cl(s) + NaNO2(aq) → N2(g) + 2H2O(l) + NaCl(aq)
State and explain how the rate of formation of nitrogen would change if the same amount of
ammonium chloride was used as large lumps instead of as a fine powder.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
(2)
(Total 9 marks)
53.
Nitrogen(II) oxide reacts with hydrogen as shown by the following equation.
2NO(g) + 2H2(g) → N2(g) + 2H2O(g)
The table below shows how the rate of reaction varies as the reactant concentrations vary.
Experiment
1
2
3
4
(a)
Initial [NO] /
mol dm–3
0.100
0.100
0.200
0.300
Initial [H2] / mol
dm–3
0.100
0.200
0.100
0.100
Initial rate /
mol N2 dm–3 s–1
2.53×10–6
5.05×10–6
10.10×10–6
22.80×10–6
Determine the order of reaction with respect to NO and with respect to H2.
Explain how you determined the order for NO.
NO ..............................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
H2 ................................................................................................................................
.....................................................................................................................................
(3)
(b) Write the rate expression for the reaction.
23
.....................................................................................................................................
(1)
(c)
Calculate the value for the rate constant, including its units.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(d)
A suggested mechanism for this reaction is as follows.
H2 + NO
X fast step
X + NO → Y + H2O slow step
Y + H2 → N2 + H2O fast step
State and explain whether this mechanism agrees with the experimental rate expression in (b).
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(4)
(e)
Explain why a single step mechanism is unlikely for a reaction of this kind.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(f)
Deduce how the initial rate of formation of H2O(g) compares with that of N2(g) in experiment 1. Explain
your answer.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
24
(2)
54.
(a)
Define the term average bond enthalpy, illustrating your answer with an equation for methane, CH4.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
(b) The equation for the reaction between methane and chlorine is
CH4(g) + Cl2(g) → CH3Cl(g) + HCl(g)
Use the values from Table 10 of the Data Booklet to calculate the enthalpy change for this reaction.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
(c)
Explain why no reaction takes place between methane and chlorine at room
temperature unless the reactants are sparked, exposed to UV light or heated.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(d) Draw an enthalpy level diagram for this reaction.
(2)
(Total 10 marks)
55. (a)
Identify two features of colliding molecules that react together in the gas phase.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
25
(b)
For many reactions, the rate approximately doubles for a 10°C rise in temperature.
State two reasons for this increase and identify which of the two is the more important.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
56.
(a)
Define the term rate of reaction.
...................................................................................................................................
...................................................................................................................................
(1)
(b) The reaction between gases C and D is slow at room temperature.
(i)
Suggest two reasons why the reaction is slow at room temperature.
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
(2)
(ii) A relatively small increase in temperature causes a relatively large increase in the rate of this
reaction. State two reasons for this.
.........................................................................................................................
.........................................................................................................................
(2)
(iii)
Suggest two ways of increasing the rate of reaction between C and D other than increasing
temperature.
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
(2)
(Total 7 marks)
57.
The oxidation of nitrogen monoxide takes place as follows:
2NO(g) + O2(g)  2NO2(g)
The following experimental data was obtained at 101.3 kPa and 298 K.
26
Experiment
Initial [NO] / mol dm–3
Initial [O2] / mol dm–3
Initial rate / mol dm–3 s–1
1
3.50×10–2
1.75×10–2
3.75×10–3
2
3.50×10–2
3.50×10–2
7.50×10–3
3
7.00×10–2
7.00×10–2
6.00×10–2
(a)
Deduce the order of reaction with respect to O2.
...................................................................................................................................
...................................................................................................................................
(1)
(b) Deduce the order of reaction with respect to NO.
...................................................................................................................................
...................................................................................................................................
(1)
(c)
State the rate expression for the reaction.
...................................................................................................................................
(1)
(d)
Calculate the value of the rate constant and state the units.
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
(2)
(e)
Suggest a possible mechanism that is consistent with the rate expression. Indicate which of the steps is
the rate-determining step.
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
(3)
(Total 8 marks)
58.
An equation for the decomposition of substance A is
2A  2B + C
A graph showing the change in concentration of A against time as the reaction proceeds at a particular
temperature is shown below.
27
0.10
0.09
0.08
0.07
0.06
[A] /
0.05
mol dm–3
0.04
0.03
0.02
0.01
0
1000
2000
3000
4000
5000
Time / s
(a)
Define the term half-life of reaction.
...................................................................................................................................
...................................................................................................................................
(1)
(b) Use the graph to measure values of half-life of reaction, starting from
time = zero ................................................................................................................
time = 1000 s ............................................................................................................
(2)
(c)
Deduce the order of the reaction with respect to A, giving a reason for your choice, and write the rate
expression for the reaction.
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
(3)
(d) For a different reaction, between compounds D and E, the rate expression is
rate = k[D]2[E]
Calculate the value of k, including units, for the reaction when the concentrations of both D and E are
1.35×10–2 mol dm–3 and the reaction rate is 3.75×10–5 mol dm–3 min–1.
(3)
(Total 9 marks)
28
59.
The reaction between two substances A and B
A+BC+D
has the following rate expression:
rate = k [B]
Draw the graphical representation of:
[A] against time
[B] against time
[B]
[A]
time
time
rate against [A]
rate against [B]
rate
rate
[A]
[B]
(Total 3 marks)
60.
In a particular experiment, various concentrations of HI(aq) are reacted with a constant H2O2(aq) concentration
according to the following equation:
H2O2(aq) + 2HI(aq)  I2(aq) + 2H2O(I)
A graph of [HI] against time is as
follows:
29
16.0
14.0
[HI] / mol dm–3 10 –2
12.0
10.0
8.0
6.0
4.0
2.0
0
(a)
20
40
60
80
Time / sec
100
120
140
160
Use the graph to deduce the order of reaction with respect to HI. Give a reason for your answer.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(b) The order with respect to H2O2 is the same as HI. Deduce the rate expression for this reaction.
....................................................................................................................................
....................................................................................................................................
(1)
(c)
Determine the half-life of the reaction from the graph and calculate the value for the rate constant.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
30
(2)
61.
(a)
The table below shows kinetic data for the following reaction
C+DE+F
(i)
Experiment
[C] / mol dm–3
[D] / mol dm–3
Initial rate
/ mol dm–3 min–1
1
2.0×10–3
3.0×10–3
1.0×10–6
2
4.0×10–3
3.0×10–3
2.0×10–6
3
6.0×10–3
6.0×10–3
3.0×10–6
Deduce the order of reaction with respect to both C and D, giving a reason in each case.
C ......................................................................................................................
.........................................................................................................................
.........................................................................................................................
D ......................................................................................................................
.........................................................................................................................
.........................................................................................................................
(4)
(ii) Deduce the rate expression for this reaction.
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
(1)
(iii)
Use data from Experiment 1 to calculate a value for the rate constant for this reaction and deduce
its units.
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
(3)
(b) Define the term half-life and calculate the half-life for a first-order reaction with a rate constant of
3.310–2 min–1.
....................................................................................................................................
....................................................................................................................................
31
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(Total 10 marks)
62.
Nitrogen(II) oxide reacts with hydrogen according to the following equation:
2NO(g) + 2H2(g) → N2(g) + 2H2O(g)
The table shows how the rate of reaction varies as the concentrations of the reactants are changed.
(a)
Experiment
Initial [NO] /
mol dm–3
Initial [H2] /
mol dm–3
Initial rate /
mol (N2) dm–3 s–1
1
0.100
0.100
253×10–6
2
0.100
0.200
5.05×10–6
3
0.200
0.100
1.01×10–5
4
0.300
0.100
2.28×10–5
Determine the order of reaction with respect to H2 and with respect to NO.
H2 ................................................................................................................................
NO ..............................................................................................................................
(2)
(b)
Write the rate expression for the reaction.
.....................................................................................................................................
(1)
(c)
Calculate the value for the rate constant, and state its units using the data from experiment 1.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(d)
A suggested mechanism for this reaction is as follows.
H2 + NO
X
X + NO → Y + H2O
Y + H2 → N2 + H2O
fast step
slow step
fast step
State and explain whether this mechanism agrees with the experimental rate expression in (b).
.....................................................................................................................................
.....................................................................................................................................
32
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(4)
(e)
Explain why a single step mechanism is unlikely for a reaction of this kind.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(f)
Deduce and explain how the initial rate of formation of H2O compares with that of N2.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(Total 13 marks)
1.
C
71.
D
72.
C
73.
D
74.
C
75.
C
76.
B
77.
C
78.
C
79.
D
80.
B
81.
A
82.
C
83.
C
84.
A
85.
D
86.
C
87.
B
64.B
65. C 66. D
67.B
68.C 69. D 70. B
33
88.
A
89.
A
90.
A
91.
C
92.
D
93.
B
94.
B
95.
D
96.
B
97.
A
98.
C
99.
(i)
Number
of
molecules /
frequency
T1
T2
Ea
Energy
both axes correctly labelled;
(ii)
T2 peak/lower;
and to right of T1;
Area under graph is not important.
3
rate increased/changes;
as more molecules with ≥ Ea;
No explicit reference to graph required.
2
[5]
100. (i)
the power of a reactant’s concentration in the rate equation/sum of
powers of concentration/rate = k[X]n, where n = order of reaction;
Must be in terms of powers of concentration.
(ii) experiment 1—2 : [X] doubles and rate×4;
2nd order for X;
experiment 2—3 : [Y] doubles and rate×2;
1st order for Y;
(iii) rate = k[X]2[Y](ECF from (ii))
for experiment 1, 1.0×10–2 = k (0.25)2(0.25);
k = 0.64;
mol–2 dm6 s–1;
Allow ECF from rate expression.
(iv) rate = 0.64[0.40]2[0.60];
= 0.061;
Final answer to 2 sig figs only.
1
4
4
2
34
Allow ECF from (iii).
[11]
101. (i)
(ii)
CaCO3(s) + 2H+(aq)  Ca2+(aq) + H2O(l) + CO2(g)
States not required, accept molecular equation.
rate decreases with time;
as concentration decreases so fewer (successful) collisions;
draw tangent to the curve at time t;
rate = slope or gradient;
1
4
(iii)
Volume of
CO2 produced
i
orig
nal
II
I
Time
I.
(less CO2 because) amount of HCl is limiting and half the
orginal/OWTTE;
II.
(same amount of CO2 because) amount of HCl is the same;
curve less steep because less frequent (accept fewer) collisions
Awarded last mark if in either I or II.
5
[10]
102. (i)
the increase in the concentration of a product/decrease in the
concentration of a reactant per unit time
1
(ii)
s–1/min–1 etc.
1
(iii)
no effect (as [OH–] does not appear in the rate expression)
1
(iv)
first order/one
1
(v)
8.0 seconds (since four half-lives elapse)
1
[5]
103. (a)
measure volume of carbon dioxide/CO2/gas produced/measure pH;
4
starts at origin and levels off
measure mass of chemicals/apparatus;
35
starts high and decreases
Graph should show increase as reaction progresses
(as HCl is consumed).
(b)
Method 1
use powdered MgCO3/OWTTE;
particles collide more frequently/increased surface area/OWTTE;
Method 2
increase (reaction) temperature/heat/warm;
more of the collisions are successful/more particles with E > Ea/OWTTE;
Method 3
increase acid concentration;
more frequent (reactant) collisions;
Method 4
add catalyst;
lowers activation energy/Ea/OWTTE;
Award [2] each for any three methods
(c)
(i)
(ii)
6 max
stays the same;
MgCO3 was already in excess;
2
stays the same;
same quantities of reactants used;
2
[14]
104. (i)
(ii)
(iii)
reversible reaction/reaction may proceed in either direction
(depending on reaction conditions) equilibrium/dynamic equilibrium;
1
no effect;
catalyst will speed up both forward and reverse reactions (equally)/
increase the rate at which equilibrium is achieved;
2
acidity: no effect;
equilibrium shifts to the right;
Kc: no change;
3
[6]
105. (a)
1/first order;
rate is (directly) proportional to concentration of oxygen/OWTTE;
2
(b)
rate
[NO(g)]
correct axes;
correct shape curve;
(c)
(d)
3/third order;
Allow ECF from (a) and (b).
overall effect on rate = 4× 12 /doubled/×2;
[NO(g)] doubled, rate =×4/quadrupled;
[O2(g)] halved, rate =×1/halved;
Allow ECF from (a) and (b).
2
1
3
36
(e)
rate = k[NO(g)]2 [O2(g)];
k
rate
6.3 104
;

[ NO ( g )]2 [O2 ( g )] (3.0 10 2 ) 2 (1.0 10 2 )
= 70;
mol–2 dm6 s–1;
Allow ECF.
State symbols not needed.
4
[12]
106. (i)
(ii)
2ICl + H2  I2 + 2HCl;
1
ICl order
1;
because doubling [ICl] doubles rate (when [H2] constant);
H2 order
2;
because halving [H2] quarters rate (when [ICl] constant);
or doubling [H2] quadruples rate (when [ICl] constant);
(iii)
(iv)
(v)
rate = k [ICl][H2]2;
ECF from (ii).
4
1
k = 5.00×103÷0.100×0.05002 = 20;
mol2 dm6 s1;
ECF from (iii).
2
rate = 20×0.200×0.1002 = 4.00×102 (mol dm3 s1);
ECF from (iii).
1
[9]
107. (a)
(b)
(i)
it relates to the geometric requirements of the reaction/orientation
of reactants on collision/OWTTE;
1
(ii)
minimum energy needed for reactants to react (on collision)/OWTTE;
1
(iii)
k measured at different values of temperature;
graph plotted of ln k against 1/T;
intercept on y-axis is ln A;
A = eintercept;
measured slope of graph =  Ea/R;
Ea = – R×gradient;
Award [1] each for any five.
(i)
homogeneous catalyst is in same phase as reactants and heterogeneous
catalyst is in different phase from reactants;
(ii)
5
1
4
Ea
Ecat
CH2CH 2  Cl 2
H
CH 2ClCH 2Cl
OR
37
Ea
H
Ecat
CH2CH 2  Cl2
H
CH 2ClCH2 Cl
reactants line higher than product line (labels not needed);
ΔH label;
Ea label;
Ecat label;
[12]
108. (a)
(b)
(c)
change of concentration/mass/amount/volume/of a reactant/product with time;
Do not accept “substance”.
all the CaCO3(s) has been consumed/no further CO2(g) is produced/reaction
is complete;
Do not accept reaction has stopped or all reactants used up.
line on graph should be initially less steep/a smaller gradient and should
plateau at the same mass loss;
1
1
1
Mass loss / g
Time / minutes
(d)
(e)
there are more particles with KE greater than or equal to Ea;
collisions more frequent/more collisions per unit time/more
successful/forceful collisions per unit time;
the rate increases;
1.00×103 (mol cm3 s1)
Ignore units even if wrong.
Apply 1(sf).
3
1
[7]
109. (a)
order of NO: second/2 - [NO] doubled, rate×4/OWTTE;
order of Br2: first/1 - as [Br2] doubled, rate of reaction doubled/OWTTE;
Reason needed for each mark.
2
38
(b)
(c)
(d)
rate = k [NO]2[Br2];
Allow ECF from (a).
1
3.20×103 = k(2.00×102)2×5.00×103
k = 1.60×103;
dm6 mol2 s1;
Allow ECF from (b).
2
(i)
no effect/K changes only with temperature/OWTTE;
1
(ii)
decrease (by a factor of 2);
1
(e)
Ea
E a (cat)
E a without catalyst
HR/E R
Enthalpy of
reactants
E a with catalyst
HP/EP
Enthalpy of
products
Time
curve clearly showing Ea without catalyst (Ea);
curve clearly showing Ea with catalyst (Ea(cat));
labelling for x axis;
3
Accept time/progress of reaction/course of reaction/OWTTE.
Award [2 max] if an enthalpy level diagram for an endothermic reaction has
been correctly drawn.
[10]
39
Number/Fraction of Molecules
110. (i)
T1
T2 > T 1
T2
Energy/speed
T2 peak lower/T1 higher;
T2 peak at higher energies/T1 curve at lower energies;
Maximum [1] if axes not labeled correctly
(ii)
(iii)
2
minimum energy required to react/energy difference between
reactants and transition state;
1
makes the reaction go faster;
because it lowers the activation energy/Ea;
2
[5]
111. (i)
a curve showing concentration decreases with time;
1
i.e.
[acid]
Time
No penalty if curve reaches x axis
Do not accept a straight line
(ii)
slope decreases;
1
(iii)
rate decreases;
fewer collisions per unit time;
2
[4]
112. (i)
rate = k[CH3COCH3][H+];
rate = k[CH3COCH3]2;
rate = k[H+]2;
(ii)
3
+
[CH3COCH3] doubles, rate doubles and [H ] doubles, rate doubles;
[Br2] double, no effect on rate;
OR
[CH3COCH3] doubles, rate quadruples;
[Br2] doubles/[H+] doubles, no effect on rate;
OR
40
[H+] doubles, rate quadruples;
[Br2] doubles/[CH3COCH3] doubles, no effect on rate;
2
The answer given must correspond to the selected expression in (i).
(iii)
constant half-life;
at least two sets of data to justify statement;
2
3
e.g. [ ] from 1.6 to 0.8 mol dm , 10s; 0.8 to 0.4, 10s; 0.4 to 0.2, 10s.
(iv)
decrease in the colour of the bromine/OWTTE;
catalyst;
increases rate/speeds up reaction;
by lowering Ea/activation energy (by providing an alternate pathway);
4
[11]
113. (a)
replacement/substitution of atom/group by another (atom/group);
by species with lone pair of electrons/attracted to electron
deficient part of molecule/positive centre/δ+ carbon atom;
2
(b)
1;
1
(c)
0;
rate not affected by change in [OH–]/OWTTE;
2
(d)
rate = k[C4H9Br] (ECF from (b) and (c));
1
(e)


k   rate  = 0.2;
[C
H
Br]
4 9


min–1;
2
Allow ECF from (d).
(f)
C4H9Br  C4H9++ Br–/in equation with curly arrows;
C4H9+ + OH–  C4H9OH/in equation with curly arrows;
2
No penalty if primary structure is shown. No credit for SN2 mechanism, except
by ECF
from (d).
(g)
the slowest step in the reaction;
the first step (however described);
2
the number of reactant molecules/species in the rate-determining step;
1 (ECF from SN2 mechanism in (f));
2
(h)
[14]
114. (a)
(b)
(i)
it is decreasing;
less frequent collisions/fewer collisions per second or (unit) time;
2
(ii)
reactant(s) used up/reaction is complete;
Do not accept reaction reaches equilibrium.
1
(i)
it would increase;
Accept a quantitative answer such as “doubles”.
1
(ii)
more frequent collisions;
collisions or molecules have more
energy (OWTTE); more molecules with energy  Ea;
3
rate would be lower;
smaller surface area;
2
(iii)
[9]
115. (a)
(b)
(order with respect to) NO = 2;
(order with respect to) H2 = 1;
rate increases×4 when [NO] doubles/OWTTE;
3
rate = k[NO]2[H2];
1
41
(c)
(2.53×10–6 mol dm–3 s–1 = k (0.100 mol dm–3)2(0.100 mol dm–3))
k = 2.53×10–3;
1
mol –2 dm6 s–1;
ECF from (b).
(d)
1
agrees/yes;
slow step depends on X and NO;
X depends on H2 and NO;
(so) NO is involved twice and H2 once;
Overall equation matches the stoichiometric equation;
Award [1] each for any three of the four above.
OWTTE
ECF for “no”, depending on answer for (b).
4 max
Or
(e)
(f)
agrees/yes;
X = constant;
and
H 2 NO
rate of slow step = k [X][NO]
= k [H2][NO]2;
ECF for “no”, depending on answer for (b).
4
reaction involves four molecules;
statistically/geometrically unlikely;
2
the rate of formation of H2O(g) = 2×rate for N2(g);
because 2 moles H2O formed with 1 mole N2/OWTTE;
2
[14]
116. (a)
(b)
(c)
energy for the conversion of a gaseous molecule into (gaseous) atoms;
(average values) obtained from a number of similar bonds/compounds/OWTTE;
CH4(g) → C(g) + 4H(g);
State symbols needed.
(bond breaking) = 1890/654;
(bond formation) = 2005/769;
enthalpy = –115(kJ mol–1)
Allow ECF from bond breaking and forming.
Award [3] for correct final answer.
Penalize [1] for correct answer with wrong sign.
molecules have insufficient energy to react (at room temperature)/
wrong collision geometry/unsuccessful collisions;
extra energy needed to overcome the activation energy/Ea for the reaction;
3
3
2
(d)
Ea
energy
reactants
products
reaction path
exothermic shown;
activation energy/Ea shown;
Allow ECF from (b).
2
42
[10]
117. (a)
(b)
molecules must have sufficient/minimum energy/energy ≥ activation energy;
appropriate collision geometry/correct orientation;
2
increased frequency of collisions/collisions more likely;
Not just “more collisions”, there must be a reference to time.
increased proportion of molecules with sufficient energy to react/E ≥ Ea;
Not “activation energy is reduced”.
Proportion of molecules with E ≥ Ea is more important;
(dependent on correct second marking point);
3
[5]
118. (a)
(b)
increase in product concentration per unit time/decrease in reactant concentration
per unit time;
1
Accept change instead of increase or decrease.
(i)
(ii)
(iii)
high activation energy/not enough molecules have Ea/OWTTE;
incorrect collision geometry/OWTTE;
infrequent collisions;
Award [1] for any two reasons.
more energetic collisions/more molecules have (energy ) Ea;
more frequent collisions/collide more often;
add a catalyst;
increase the (total) pressure/decrease the volume of the container;
increase the concentration of C (or D);
Do not accept surface area.
Award [1] for any two.
2
2
2
[7]
119. (a)
first order (with respect to O2);
1
(b)
second order (with respect to NO);
1
(c)
rate = k[NO]2[O2];
Allow ECF from parts (a) and (b).
1
(d)
k
3.75103
(3.50102 ) 2 (1.75102 )
 1.75102 ;
dm6 mol–2 s–1;
Award [1] mark for the answer and [1] mark for units.
Allow ECF from part (c).
(e)
NO + NO
2
N2O2;
N2O2 + O2  2NO2;
second step is rate determining step;
Allow ECF from part (c).
OR
NO + O2
NO3;
NO3 + NO  2NO2;
second step is rate determining step;
Allow ECF from part (c).
3
[8]
120. (a)
time for reactant concentration to halve/OWTTE;
Accept “time for mass to halve”.
1
43
(b)
1000 s;
1000 s;
2
Accept 900-1100 s.
(c)
(d)
first order;
constant half-life;
rate = k[A];
Allow ECF for rate expression from stated order.
k
3
3.75 105
rate
/
;
[D]2 [E] (1.35 102 ) 3
= 15.2;
Accept answer in range 15.2 to 15.3.
mol2 dm6 min1;
3
[9]
121. ([A] against time) - straight line with negative gradient;
Accept any decreasing curve
([B] against time) - decreasing curve;
Award [1] unless half - lives clearly not constant
(rate against [A]) - any horizontal straight line;
(rate against [B]) - straight line through origin;
Award [3] for all four correct, award [2] for any three correct and [1] for any
two correct.
[3]
122. (a)
first order;
constant half-life;
(b)
rate = k[HI][H2O2];
ECF from(a).
(c)
47 sec;
2
1
Accept answer in range 45 to 49.


 t 1  0.693   0.015;

k 
 2
Accept answer in range 0.014-0.015.
ECF from half-life.
2
[5]
123. (a)
(i)
(C)
first order;
doubling [C] doubles rate/OWTTE;
(D)
zero order;
changing [D] has no effect on rate/OWTTE;
(ii)
rate = k[C]/rate = k[C]1[D]0;
Apply ECF from (a)(i).
(iii)
k=
1
rate 1.0 106
/
;
[C ] 2.0 103
= 5.0×104;
min1;
Apply ECF from (a)(ii).
(b)
4
3
time for half of (amount/concentration of) reactant to react/disappear;
44
t
1
( = 0.693÷0.033) = 21 min;
2
Units needed for second mark.
2
[10]
124. (a)
(order with respect to) H2 = 1;
(order with respect to) NO = 2;
(b)
rate = k[H2][NO]2;
ECF from (a).
(c)
(2.53×10−6 mol dm–3 s–1 = k(0.100 mol dm−3)(0.100 mol dm–3)2)
k = 2.53×10–3;
mol−2 dm6 s–1;
ECF from (b).
(d)
2
1
2
agrees/yes;
slow step depends on X and NO;
(so) NO is involved twice and H2 once;
overall equation matches the stoichiometric equation/OWTTE;
ECF for “no”, depending on answer for (b).
OR
agrees/yes;
[X]
and
= constant;
[H 2 ][NO]
rate of slow step = k[X][NO];
but X depends on H2 and NO;
rate of slow step = k[H2][NO]2;
Award [1] each for any three of the four above.
ECF for “no”, depending on answer for (b).
(e)
(f)
4 max
reaction involves four molecules;
statistically/geometrically unlikely;
2
the rate of formation of H2O = 2×rate for N2;
because 2 moles H2O formed with 1 mole N2/OWTTE;
2
[13]
45