IB Chemistry – SL
Topic 6 Questions
1.
2.
3.
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
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?
4.
5.
6.
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
A.
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
Which of the following is (are) altered when a liquid at its boiling point is converted to a gas at
the same temperature?
I.
The size of the molecules
II.
The distance between the molecules
III.
The average kinetic energy of the molecules
A.
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.
mol dm–3
B.
mol time–1
C.
dm time–1
D.
mol dm–3 time–1
2
7.
Which of the quantities in the enthalpy level diagram below is (are) affected by the use of a
catalyst?
Enthalpy
I
II
III
Time
8.
A.
I only
B.
III only
C.
I and II only
D.
II and III only
In the Haber process for the synthesis of ammonia, what effects does the catalyst have?
A.
B.
C.
D.
9.
10.
Rate of formation of NH3(g)
Increases
Increases
Increases
No change
Amount of NH3(g) formed
Increases
Decreases
No change
Increases
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
3
11.
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.
12.
13.
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
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
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
4
14.
15.
16.
17.
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
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 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
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
5
What change in the experiment could give line 2?
18.
A.
The same mass of magnesium in smaller pieces
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?
Enthalpy
I
II
III
Time
19.
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
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.
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
(4)
6
(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)
20.
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.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(6)
7
(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)
21.
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)
8
22.
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)
(d)
Explain in terms of the collision theory what would happen to the rate if the reaction was
conducted at 50C.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
9
(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.
....................................................................................................................................
....................................................................................................................................
(1)
(Total 7 marks)
23.
(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)
24.
(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.
(2)
(Total 4 marks)
25.
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
10
(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.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
(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)
11
26.
(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)
12
27.
(a)
Identify two features of colliding molecules that react together in the gas phase.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(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)
(Total 5 marks)
28.
(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)
13
29.
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)
14
IB Chemistry – SL
Topic 6 Answers
1.
C
2.
B
3.
B
4.
C
5.
B
6.
D
7.
C
8.
C
9.
C
10.
D
11.
A
12.
B
13.
A
14.
A
15.
C
16.
B
17.
B
18.
A
19.
(i)
CaCO3(s) + 2H+(aq)  Ca2+(aq) + H2O(l) + CO2(g)
States not required, accept molecular equation.
(ii)
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)
15
Volume of
CO2 produced
orig
inal
II
I
Time
20.
(a)
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
measure volume of carbon dioxide/CO2/gas produced/measure pH;
5
4
starts at origin and levels off
measure mass of chemicals/apparatus;
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
16
add catalyst;
lowers activation energy/Ea/OWTTE;
Award [2] each for any three methods
(c)
(i)
(ii)
stays the same;
MgCO3 was already in excess;
6 max
2
stays the same;
same quantities of reactants used;
2
[14]
21.
(i)
reversible reaction/reaction may proceed in either direction
(depending on reaction conditions) equilibrium/dynamic equilibrium;
(ii)
(iii)
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]
22.
(a)
change of concentration/mass/amount/volume/of a reactant/product with time;
Do not accept “substance”.
(b)
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.
(c)
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
17
(d)
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;
(e)
1.00×103 (mol cm3 s1)
Ignore units even if wrong.
Apply 1(sf).
3
1
[7]
(i)
Number/Fraction of Molecules
23.
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]
24.
(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
18
(ii)
slope decreases;
1
(iii)
rate decreases;
fewer collisions per unit time;
2
[4]
25.
(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.
(i)
it would increase;
Accept a quantitative answer such as “doubles”.
(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)
1
1
[9]
26.
(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
[10]
19
27.
(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);
28.
(a)
(b)
increase in product concentration per unit time/decrease in reactant concentration
per unit time;
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.
3
1
2
2
2
[7]
29.
([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.
20