SL IB2 Chemistry Equilibrium (Topic 7) Summative 2015
Name:______________
Multiple Choice: Choose the most correct answer and mark the appropriate box on the
answer sheet.
1.
2.
The equilibrium between nitrogen dioxide, NO2, and dinitrogen tetroxide, N2O4, is shown
below.
2NO2(g)
N2O4(g)
Kc = 0.01
What happens when the volume of a mixture at equilibrium is decreased at a constant
temperature?
I.
The value of Kc increases
II.
More N2O4 is formed
[ NO 2 ]
III. The ratio of
decreases
[N 2 O 4 ]
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
For the following reaction Kc = 1.0 × 10–5 at 30 °C.
2NOCl(g)
2NO(g) + Cl2(g)
Which relationship is correct at equilibrium at this temperature?
3.
A.
B.
The concentration of NO equals the concentration of NOCl.
The concentration of NOCl is double the concentration of Cl2.
C.
D.
The concentration of NOCl is much greater than the concentration of Cl2.
The concentration of NO is much greater than the concentration of NOCl.
The reaction below represents the Haber process for the industrial production of ammonia.
N2(g) + 3H2(g)
2NH3(g)
∆HO = –92 kJ
The optimum conditions of temperature and pressure are chosen as a compromise between
those that favor a high yield of ammonia and those that favor a fast rate of production.
Economic considerations are also important. Which statement is correct?
A.
B.
C.
D.
4.
A higher temperature would ensure higher yield and a faster rate.
A lower pressure would ensure a higher yield at a lower cost.
A lower temperature would ensure a higher yield and a faster rate.
A higher pressure would ensure a higher yield at a higher cost.
What is the effect of an increase of temperature on the yield and the equilibrium constant
for the following reaction?
2H2(g) + CO(g)
CH3OH(l)
∆HO = –128 kJ
Yield
A.
B.
C.
D.
Increases
Increases
Decreases
Decreases
Equilibrium
constant
Increases
Decreases
Increases
Decreases
Name:______________
SL IB2 Chemistry Equilibrium (Topic 7) Summative 2015
5.
What is the equilibrium constant expression, Kc, for the following reaction?
N2O4(g)
6.
2NO2(g)
[NO 2 ]
[N 2 O 4 ]
A.
Kc =
B.
Kc =
C.
Kc =
D.
Kc = [NO2][N2O4]2
[NO 2 ] 2
[N 2 O 4 ]
[NO 2 ]
[N 2 O 4 ] 2
Which statement is correct for a crystal of iron(II) sulfate in a state of equilibrium with a
saturated solution of iron(II) sulfate?
A.
B.
C.
D.
7.
The color of the solution darkens as the crystal continues to dissolve.
The concentration of the iron(II) sulfate solution increases as the water evaporates.
The shape of the iron(II) sulfate crystal does not change.
The color of the solution does not change but the shape of the crystal may
change.
An increase in temperature increases the amount of chlorine present in the following
equilibrium.
PCl5(s)
PCl3(l) + Cl2(g)
What is the best explanation for this?
A.
B.
C.
D.
8.
The higher temperature increases the rate of the forward reaction only.
The higher temperature increases the rate of the reverse reaction only.
The higher temperature increases the rate of both reactions but the forward
reaction is affected more than the reverse.
The higher temperature increases the rate of both reactions but the reverse reaction is
affected more than the forward.
For the same reaction, the Kc at 278K is 2.3 x 102 and Kc at 500K is 3.4 x 103, which of the
following is true for the enthalpy of the forward reaction?
A.
B.
C.
Enthalpy
Endothermic
Exothermic
Endothermic
Value of ∆H
+
+
-
SL IB2 Chemistry Equilibrium (Topic 7) Summative 2015
Name:______________
D.
Exothermic
The sequence of diagrams represents the system as time passes for a gas phase reaction in
which reactant X is converted to product Y.
9.
Diagram 1
t = 7 seconds
Diagram 2
t = 5 minutes
Diagram
t = 10 minutes
Diagram 4
t = 5 days
Time, t
X=
Y=
Which statement is correct?
A.
B.
C.
D.
10.
At t = 5 days the rate of the forward reaction is greater than the rate of the backward
reaction.
At t = 7 seconds the reaction has reached completion.
At t = 10 minutes the system has reached a state of equilibrium.
At t = 5 days the rate of the forward reaction is less than the rate of the backward
reaction.
A reaction in a closed reaction vessel has a reaction quotient value of 4.5x102. The
equilibrium constant value of this same reaction at the same temperature is 3.3x103. Which
of the following are true about this reaction.
A. The reaction will favor the forward reaction indefinitely.
B. The reaction will favor the production of products until equilibrium is established.
C. The reaction will favor the production of more reactants until equilibrium is
established.
D. The reaction will favor the reverse reaction indefinitely.
11.
The equilibrium constant for the equilibrium between N2O4 and NO2 is 7.7x10-4 at 273K.
N2O4 (g)
2 NO2 (g)
Determine the value of Kc for the reverse reaction.
A. Kc = 7.7x10−4
B. Kc = (7.7x10−4 )2
−𝟏
C. Kc = (𝟕. 𝟕𝐱𝟏𝟎−𝟒 )
D. Kc = 7.7x104
Name:______________
SL IB2 Chemistry Equilibrium (Topic 7) Summative 2015
12.
Chloroethene, C2H3Cl, reacts with oxygen according to the equation below.
2C2H3Cl(g) + 5O2(g) → 4CO2(g) + 2H2O(g) + 2HCl(g)
What is the amount, in mol, of H2O produced when 10.0 mol of C2H3Cl and 10.0 mol of
O2 are mixed together, and the above reaction goes to completion?
A.
B.
C.
D.
4.00
8.00
10.0
20.0
13. Which compound forms hydrogen bonds in the liquid state?
A.
B.
C.
D.
C2H5OH
CHCl3
CH3CHO
(CH3CH2)3N
14. The table shows the concentrations of reactants and products during the reaction
X + 2Y → 2Z
-3
[X] / mol dm
-3
[Y] / mol dm
-3
[Z] / mol dm
At the start
4
3
0
After 10 seconds
3
1
2
The rate of a reaction can be referenced to any reactant or product. Which is a correct
statement about the rate of the reaction?
A.
B.
C.
D.
Rate = 0.3 mol dm-3 s-1 with reference to X
Rate = 1.0 mol dm-3 s-1 with reference to Y
Rate = – 0.1 mol dm-3 s-1 with reference to Y
Rate = 0.2 mol dm-3 s-1 with reference to Z
15. Iron reacts with sulfuric acid according to the equation
Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g)
Exactly 1.0 g of iron powder from the same bottle was added to separate samples of excess
sulfuric acid in two separate experiments.
3
-3
Experiment 1. Iron added to 100 cm of 1.0 mol dm H2SO4(aq)
Experiment 2. Iron added to 200 cm3 of 2.0 mol dm-3 H2SO4(aq)
Which will be the same for both reactions?
A.
B.
C.
D.
The volume of hydrogen gas evolved.
The initial rate of reaction.
The increase in temperature of the solution.
The total time taken for the reaction to finish.
End of Paper 1
Name:______________
SL IB2 Chemistry Equilibrium (Topic 7) Summative 2015
/25
SA – Equilibrium (Topic 7) Paper 2
1.
Methanol may be produced by the exothermic reaction of carbon monoxide gas and
hydrogen gas.
CO(g) + 2H2(g)
CH3OH(g)
∆HO = –103 kJ
(a) State the equilibrium constant expression, Kc, for the production of methanol.
Kc =)
[CH 3 OH]
;
[CO][H 2 ] 2
Do not award mark if incorrect brackets are used or brackets are missing.
1
(1)
(b) State and explain the effect of changing the following conditions on the amount of methanol
present at equilibrium:
(i)
increasing the temperature of the reaction at constant pressure.
(i) amount (of methanol)/product decreases / less methanol;
(forward reaction) exothermic / reverse reaction endothermic / OWTTE;
........................................................................................................................................................
(2)
(ii)
increasing the pressure of the reaction at constant temperature.
amount (of methanol)/product increases / more methanol;
3 gas molecules/mol → 1 / decrease in volume / fewer gas
molecules on right hand side/products / more gas molecules
on left hand side/reactants;
........................................................................................................................................................
(2)
2.
If the equilibrium constant for the reaction, 2HI (g)
temperature.
H2(g) + I2(g) is 0.04 at a certain
Calculate the value of the equilibrium constant for the following reaction at the same
temperature:
½ H2(g) + ½ I2(g)
HI (g)
1
The reaction is reversed and halved, Kc’ = 1/√𝐾𝑐 or √𝐾𝑐 −1 = √(0.04) = 5 (1 sig fig)
(2)
SL IB2 Chemistry Equilibrium (Topic 7) Summative 2015
3.
Name:______________
Consider the following reaction taking place at 375 °C in a 1.00 dm3 closed container.
Cl2(g) + SO2(g)
∆HO = –84.5 kJ
SO2Cl2(g)
(a) Deduce the equilibrium constant expression, Kc, for the reaction.
[SO 2 Cl 2 ]
;
[Cl 2 ][SO 2 ]
Ignore state symbols.
Square brackets [ ] required for the equilibrium expression.
(b) (Kc) =
(c) (1)
(b)
If the temperature of the reaction is changed to 300 °C, predict, stating a reason in
each case, whether the equilibrium concentration of SO2Cl2 and the value of Kc will
increase or decrease.
value of Kc increases;
[SO2Cl2] increases;
decrease in temperature favours (forward) reaction which is exothermic;
Do not allow ECF.
........................................................................................................................................................
(3)
(c)
If the volume of the container is changed to 1.50 dm3, predict, stating a reason in
each case, how this will affect the equilibrium concentration of SO2Cl2 and the value
of Kc.
no effect on the value of Kc / depends only on temperature;
[SO2Cl2] decreases;
increase in volume favours the reverse reaction which has more
gaseous moles;
Do not allow ECF.
........................................................................................................................................................
(3)
4.
The equation for the main reaction in the Haber process is:
N2(g) + 3H2(g)
(a)
2NH3(g)
∆H is negative
State and explain the effect on the equilibrium yield of ammonia with increasing the
pressure and the temperature.
Increasing the pressure:
Yield increases / equilibrium moves to the right / more ammonia;
4 gas molecules → 2 / decrease in volume / fewer gas molecules
on right hand side;
Increasing the temperature:
Yield decreases / equilibrium moves to the left / less ammonia;
Exothermic reaction / OWTTE;
.......................................................................................................................................................
SL IB2 Chemistry Equilibrium (Topic 7) Summative 2015
Name:______________
(4)
(b)
At a certain temperature and pressure, 1.1 dm3 of N2(g) reacts with 3.3 dm3 of H2(g).
Calculate the volume of NH3(g), that will be produced.
2.2 (dm3);
1
Penalize incorrect units.
........................................................................................................................................................
(1)
(c)
Draw the Lewis structure of ammonia and state the shape of the molecule and its
bond angles.
Accept any combination of dots/crosses and lines to represent
electron pairs.
(trigonal/triangular) pyramid;
Allow 3D representation using wedges and dotted bonds of
trigonal pyramidal molecule.
107°;
3
Accept any angle between 105º and 108.5º.
No ECF for shape based on incorrect Lewis structure
......................................................................................................................................
(3)
(d)
The conjugate acid of ammonia is the ammonium ion, NH4+. Draw the Lewis
structure of the ammonium ion and deduce its shape and bond angles.
Charge needed for mark.
tetrahedral;
Allow a 3D representation using wedges and dotted bonds
of tetrahedral molecule.
109.5°/109°/109° 28';
3
No ECF for shape based on incorrect Lewis structure.
(3)
SL IB2 Chemistry Equilibrium (Topic 7) Summative 2015
Name:______________
End of Paper 2
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