Download Chemical Equilibrium Review Ch 13-14 2015

AMHS AP CHEMISTRY – Equilibrium Review
Name ________________________
Complete the following problems on additional sheets of paper. Prior to solving the problem, write out
the chemical principle or concept you will utilize to answer the question.
Example: A problem addresses the expected change in the value of “K” required when writing an
equilibrium expression for a chemical reaction whose stoichiometry was changed from the original
balanced chemical equation.
Chemical Principle: Changing the stoichiometry will be reflected in raising the original equilibrium value
to the power of the stoichiometric change.
Then solve the problem showing all pertinent work!
Chapter 13 - Equilibrium
1. Carbon monoxide and hydrogen react according to the following equation:
CO(g) + 3H2(g)  CH4(g) + H2O(g)
When 1.000 mol CO and 3.000 mol H2 are placed in a 10.00-L vessel at 927.0°C (1200.K) and allowed to
come to equilibrium, the mixture is found to contain 0.387mol H2O. What is the molar composition of the
equilibrium mixture? (That is, how many moles of each substance are present?)
2. Equilibrium Expressions
(a) Write the equilibrium constant expression Kc for catalytic methanation given the following
methanation reaction.
CO(g) + 3H2(g)  CH4(g) + H2O(g)
(b) Write the equilibrium constant expression Kc for the reverse of the previous reaction
CH4(g) + H2O(g)  CO(g) + 3H2(g)
(c) Write the equilibrium constant expression Kc for the synthesis of ammonia.
N2(g) + 3H2(g) 
3(g)
(d) Write the equilibrium expression Kc when the equation for the previous reaction is written:
½ N2(g) + 3/2 H2(g) 
3(g)
3. Hydrogen iodide, HI, decomposes at moderate temperatures according to the equation:
2HI(g) 
2(g) + I2(g)
The amount of I2 in the reaction mixture can be determined from the intensity of the violet color of
I2…the more intense the color, the more I2 in the reaction vessel. When 4.00mol HI was placed in a 5.00L
vessel at 458°C, the equilibrium mixture was found to contain 0.442mol I2. What is the value of Kc for
the decomposition of HI at this temperature?
4. Phosphorus pentachloride dissociates on heating: PCl5(g) 
If Kc equals 3.28 × 10-2 at 191°C, what is Kp at this temperature?
3(g)
+ Cl2(g)
5. Quicklime (calcium oxide, CaO) is prepared by heating a source of calcium carbonate, CaCO3, such as
limestone or seashells as noted by the following balanced equation:
CaCO3(s) CaO(s) + CO2(g)
(a) Write the expression for Kc.
(b) You can write the equilibrium constant expression for a physical equilibrium, such as vaporization, as
well as for a chemical equilibrium. Write the expression for Kc for the vaporization of water.
H2O(l)  2O(g)
6. A 50.0L reaction vessel contains 1.00mol N2, 3.00mol H2, and 0.500mol NH3.
The balanced equation is: N2(g) + 3H2(g) 
3(g) and the Kc for this reaction is 0.500 at 400.°C.
Will more ammonia, NH3, be formed or will it dissociate when the mixture goes to equilibrium at 400.°C?
7. A gaseous mixture contains 0.30mol CO, 0.10mol H2, and 0.020mol H2O, plus an unknown amount of
CH4, per liter. This mixture is at equilibrium at 1200.K.
CO(g) + 3H2(g) CH4(g) + H2O(g)
The equilibrium constant Kc = 3.92. What is the equilibrium concentration of CH4 in this mixture?
8. The reaction CO(g) + H2O(g) 
2(g) + H2(g) is used to synthesize hydrogen in mixtures of CO
and H2O. Suppose you start with 1.00 mol each of carbon monoxide and water in a 50.0L vessel. How
many moles of each substance are in the equilibrium mixture at 1000.°C? The equilibrium constant Kc at
this temperature is 0.58.
9. Hydrogen and iodine react according to the equation H2(g) + I2(g) 
2
and 2.00mol I2 are placed in a 1.00L vessel.
(a) How many moles of substances are in the gaseous mixture when it comes to equilibrium at 458°C?
The equilibrium constant Kc at this temperature is 49.7.
(b) Predict the direction of reaction when H2 is removed from a mixture (lowering its concentration) in
which equilibrium has been established.
11. Look at each of the following equations and decide whether an increase of pressure obtained by
decreasing the volume will increase, decrease, or have no effect on the amounts of products.
(a) CO(g) + Cl2(g) COCl2(g)
(b.) 2H2S(g) 2H2(g) + S2(g)
(c) C(graphite) + S2(g) 
2(g)
12. Carbon monoxide is formed when carbon dioxide reactions with solid carbon (graphite).
CO2(g) + C(graphite) 2CO(g)
H° = +172.5 kJ
Assume this reaction is initially at equilibrium and then predict any changes in direction that may occur
based on the following adjustments to the environment.
b) The pressure inside the container is doubled by the addition of helium gas.
c) Carbon monoxide is removed from the container.
d) The temperature of the container is decreased by 10.°C?
e) A small addition of graphite is added to the container.
f) An effective catalyst is added to the container.
Chapter 14 – Acids and Bases
1. (a) Write a chemical equation describing the ionization or dissociation in water of the following acids
and bases: HCl(aq); HBr(aq); HNO2(aq); NH3(aq); NaOH(s).
(b) Which of the following would you expect to have a significant capacity to react with a hydrated
proton: Cl−, Br−, NO 12 , NH 14 ? Justify your response(s).
2. You are provided equimolar amounts of each of the following reactants, which are then mixed.
(a) Indicate which reactant is the acid and which is the base in each of the following reactions:
(i) HC2H3O2(aq) + NaOH(aq) → NaC2H3O2(aq) + H2O(l)
(ii) ZnS(s) + 2 HCl(aq) → H2S(g) + ZnCl2(aq)
(iii) KCN(aq) + H2O(l) → KOH(aq) + HCN(aq)
(b) Determine the identity of the ion(s) expected to be in excess when the above reactions reach
equilibrium.
3. Write the conjugate acid for each of the following species:
(a) H2O
(b) OH1−
(c) CO 32 
(d) NH3
4. Write the conjugate base for each of the following species:
(a) H2O
(b) OH1−
(c) H2SO4
5. CN− reacts with water as follows:
(d) NH3
CN−(aq) + H2O(l)  HCN(aq) + OH1−(aq)
A Cl− ion does not react with water to form HCl. Which acid is stronger, HCl(aq) or HCN(aq)? Why?
What about the strength of the bases involved in the reactions?
6. A solution has a hydroxide-ion concentration of 1.5 × 10−5 M.
(a) What is the concentration of hydronium ions in this solution?
(b) What is the pH of this solution?
(c) Is the solution acidic, basic, or neutral?
7. A solution has a pH of 5.60. Calculate the hydrogen-ion concentration.
8. Calculate [H+] for a solution with a pOH of 4.75.
9. Calculate the pH of a 0.10 M HNO3 solution.
10. Calculate the pOH and pH of a 0.02 M Ba(OH)2 solution.
11. Calculate the percentage of hydroxylamine ionized in a 0.020 M hydroxylamine solution.
(Kb = 1.1×10−8 for hydroxylamine NH2OH).
12. Acetic acid is the chemical name for the common ingredient known as vinegar (HC2H3O2).
(a) Calculate the pH of a 0.015 M acetic acid solution. The value of Ka is 1.8 × 10−5 for acetic acid.
(b) Calculate the pH of a 0.150M acetic acid solution. Determine, compare and discuss the percent
dissociation for each of these solutions.
13. Explain for a triprotic acid why the following trend in equilibrium constants is observed:
Ka1 > Ka2 > Ka3
14. (a) Explain why the hydrogen-ion concentrations for a 0.10 M H3PO4 solution can be determined from
its first ionization step. The successive equilibrium constants are:
Ka1 = 7.5 × 10−3, Ka2 = 6.2 × 10−8, Ka3 = 4.8 × 10−13
(b) Calculate the pH of this solution.
(c) Determine the concentration of the HPO42-ion.
15. Classify the following aqueous solutions as neutral, basic, or acidic:
(a) KCl
(b) NH4NO3
(c) Na2CO3
(d) RbF
(e) TiBr4
16. Sodium formate (NaCOOH) dissolves 100% in solution. The Ka of formic acid (HCOOH) is 1.8×10−4.
(a) Calculate the pH of a 0.25 M solution of sodium formate.
(b) Diagram the Lewis structure of the formate ion while showing hybridizations and bond angles for all
central atoms.
17. Although NaOH and HOCl have the same formula type, Y-OH, they have different acid-base
properties. Explain why NaOH is a base and HOCl is an acid.
18. Which acid is stronger in water, chloric acid, HClO3, or chlorous acid, HClO2. Justify your answer.
19. Define a Lewis acid.
(a) Using as an example the reaction of NH3 with H2O, show that the Lewis definition of an acid is
consistent with the Bronsted-Lowry definition. (Hint: Lewis structures are very convincing when
explaining the Lewis acid-base theory!)
(b) Which reactant molecule or ion in the reaction below is the Lewis acid? Which is the Lewis base?
Ag+(aq) + 2 NH3(aq) → Ag(NH3) 2 (aq)
20. Write the hydrolysis reaction for Zn(H2O) 24  and the subsequent acid/base reaction that occurs in
water.