Unit 4
REVIEW
Unit 4
Understanding Concepts
1. The equilibrium constant for the following reaction
has a value of 279 at 1000 K.
(b) The second step in making urea involves the
decomposition of ammonium carbamate:
NH2CO2NH4(aq) 1 energy e CO(NH2)2(s) 1 H2O(g)
(urea)
2 SO2(g) 1 O2(g) e 2 SO3(g)
How could the temperature and pressure be
altered to maximize the yield of urea?
(7.3)
Use this information to calculate the value of the
equilibrium constant for the reaction
(7.2)
2 SO3(g) e 2 SO2(g) 1 O2(g)
2. Nitrogen monoxide is a pollutant produced during
the combustion of gasoline in cars. The reaction
involved is
N2(g) 1 O2(g) e 2 NO(g)
An equilibrium mixture at 2000°C contains these
concentrations:
[N2(g)] 5 0.63 mol/L; [O2(g)] 5 0.21 mol/L;
[NO(g)] 5 0.015 mol/L
6. (a) Calculate the solubility of silver chloride at 25°C.
(b) Calculate the solubility of silver chloride in
0.015 mol/L sodium chloride.
(c) Use Le Châtelier’s principle to explain why the
answers in (a) and (b) differ.
(7.3)
7. Ammonia, an important chemical used in the production of chemical fertilizers, is synthesized from its
elements according to the reaction
N2(g) 1 3 H2(g) e 2 NH3(g)
Consider the following equilibrium constants at different temperatures for this reaction.
Table 1 K at Different Temperatures
Calculate the value of the equilibrium constant for
this reaction.
(7.2)
Temp (°C)
K
473
612
3. Consider this reaction:
C(s) 1 H2O(g) e CO(g) 1 H2(g)
873
4. Methanol can be produced using the following reaction:
CO(g) 1 2 H2(g) e CH3OH(g)
DH ° 5 290.1 kJ
Suggest three ways in which to increase the methanol
concentration at equilibrium.
(7.3)
5. Urea is an important nitrogen-based fertilizer.
(a) The first step in the production of urea fertilizer is
2 NH3(g) 1 CO2(g) e NH2CO2NH4(aq) 1 energy
(ammonium carbamate)
Explain why running the reaction at high pressure
increases the yield of this reaction to almost 100%.
NEL
3.9 3 1022
1073
DH ° 5 131.3 kJ
Predict the effect, if any, of the following changes on the
equilibrium concentration of carbon monoxide, CO.
(a) increasing the concentration of hydrogen gas
(b) cooling the reaction vessel
(c) increasing the volume of the reaction vessel
(d) adding a catalyst
(e) grinding the carbon into a fine powder
(f) removing hydrogen
(g) adding inert argon gas to the reaction vessel (7.3)
4.2
Is the synthesis of ammonia endothermic or
exothermic? Explain your answer.
(7.4)
8. Nitrosyl chloride, NOCl(g), decomposes to form
nitrogen monoxide, NO(g), and chlorine gas, Cl2(g),
according to the following chemical equation:
2 NOCl(g) e 2 NO(g) 1 Cl2(g)
At 35°C the equilibrium constant, K, is 1.60 3 1025.
(a) At this temperature, are the products or reactants
favoured?
(b) Calculate the equilibrium concentration of
NOCl(g), if the equilibrium concentrations of
NO(g) and Cl2(g) are both 0.10 mol/L.
(7.5)
9. Consider the following equilibrium system:
N2O4(g) e 2 NO2(g)
(colourless)
K 5 6.13 3 1023 at 25°C
(reddish-brown)
If the molar concentration of N2O4(g) and NO2(g) are
8.00 3 1024 mol/L and 4.00 3 1023 mol/L
respectively, is the system at equilibrium? If not, what
colour change would be observed as the system shifts
to approach equilibrium?
(7.5)
Chemical Systems and Equilibrium
639
10. Consider this equilibrium:
2 SO3(g) e 2 SO2(g) 1 O2(g)
H2(g) 1 CO2(g) e H2O(g) 1 CO(g)
When 0.100 mol each of hydrogen and carbon
dioxide are introduced into a 1.00-L container at
986°C, the equilibrium concentration of carbon
monoxide is found to be 0.056 mol/L.
(a) Calculate the equilibrium concentrations of all
substances.
(b) Calculate the value of the equilibrium constant.
(7.5)
11. Phosphorus pentachloride decomposes according to
the reaction
PCl5(g) e PCl3(g) 1 Cl2(g)
When 0.60 mol of PCl5(g) are initially put into a 2.00-L
container, the equilibrium concentration of chlorine
is found to be 0.26 mol/L.
(a) Calculate the equilibrium concentration of all
substances.
(b) Calculate the value of the equilibrium constant.
(7.5)
12. Hydrogen and iodine combine to form hydrogen
iodide according to the equation,
H2(g) 1 I2(g) e 2 HI(g)
K 5 49.7 at 458°C
Calculate the equilibrium concentrations of all substances if 0.50 mol H2(g) and 0.50 mol I2(g) are initially
placed into a 5.00-L reaction vessel at 458°C.
(7.5)
13. Ammonia decomposes into its elements according to
the reaction
2 NH3(g) e N2(g) 1 3 H2(g)
K 5 1.60 3 1023 at 200°C
If the initial concentration of ammonia is 0.20 mol/L,
what are the equilibrium concentrations of all substances?
(7.5)
14. Consider the formation of hydrogen iodide from its
elements:
H2(g) 1 I2(g) e 2 HI(g)
K 5 49.7 at 458°C
If 2.00 mol of hydrogen and 1.00 mol of iodine are initially placed into a 5.00-L reaction vessel, what is the
equilibrium concentration of hydrogen iodide? (7.5)
15. Sulfur trioxide decomposes according to the following equation:
640 Unit 4
K 5 6.9 3 1027 at 1500°C
What concentration of oxygen can be expected when
0.400 mol of SO3(g) comes to equilibrium at 1500°C
in a 2.00-L vessel?
(7.5)
16. Calculate the molar solubility of calcium sulfate at
25°C.
(7.6)
17. Calculate the molar concentration of chloride ions in
a saturated solution of lead(II) chloride, PbCl2, at
25°C.
(7.6)
18. The chloride ion concentration in tap water can be
2.2 3 1024 mol/L. Will a precipitate form if 250.0 mL
of water is mixed with 250.0 mL of 0.010 mol/L silver
nitrate at SATP?
(7.6)
19. A solution is prepared by mixing 100.0 mL of
0.015 mol/L magnesium nitrate with 300 mL of
0.10 mol/L potassium fluoride at SATP. Will a
precipitate form?
(7.6)
20. Distinguish between the terms solubility and solubility product.
(7.6)
21. Name two substances that will decrease the solubility
(7.6)
of calcium sulfate, CaSO4(s) in water.
22. Predict whether the change in entropy is positive or
negative for each of the following changes. Explain
your answers.
(a) Na(s) → Na(l)
(b) Pb(NO3)2(aq) 1 2 KI(aq) →
PbI2(s) 1 2 KNO3(aq)
(c) H2O(g) 1 Cl2O(g) → 2 HOCl(g)
(d) NH4Cl(s) → NH3(g) 1 HCl(g)
(7.7)
23. Use the Gibbs-Helmholtz equation to explain qualitatively why table salt, NaCl(s), does not spontaneously
decompose into its elements at room temperature. (7.7)
24. Cold packs contain solid ammonium chloride, which
absorbs thermal energy from the water. Calculate the
standard Gibbs free energy change associated with the
dissolving of ammonium chloride and interpret the
results.
NH4Cl(s) → NH4Cl(aq)
(7.7)
25. Methane, CH4(g), is a major component of natural
gas. Calculate the value of DG° for the combustion of
methane to produce only gaseous products. What
does the value of DG ° for this reaction tell you? (7.7)
26. Use the Gibbs-Helmholtz equation and the concept
of equilibrium to calculate the normal condensation
(7.7)
point of ethanol, C2H5OH(l).
NEL