Name ______
Equilibrium Test Review
AP Chemistry
1) Which of the following statements is true?
A) When two opposing processes are proceeding at identical rates, the system is at equilibrium.
B) Catalysts are an effective means of changing the position of an equilibrium.
C) The concentration of the products equals that of reactants and is constant at equilibrium.
D) An endothermic reaction shifts toward reactants when heat is added to the reaction.
E) None of these statements is true.
2) If, at a given temperature, the equilibrium constant for the reaction 2X(g) + Y(g) ßà 3W(g) + V(g) is Kp, then the equilibrium constant for the reaction 3/2 W(g) + ½ V(g) ßà X(g) + ½ Y(g)
can be represented as:
A) 1/Kp2
B) Kp2
C) 1/Kp1/2
D) Kp1/2
3) At 500.0 K, one mole of gaseous ONCl is placed in a one-liter container. At equilibrium it is 9.0% dissociated according to the equation shown here: 2ONCl ßà 2NO + Cl2 Determine the equilibrium constant.
A) 4.4 x 10–4
B) 2.2 x 102
C) 1.1 x 102
D) 2.2 x 10–4
E) 9.1 x 10–1
4) Consider the reaction H2 + I2 ßà 2HI whose K = 54.8 at 425°C. If an equimolar mixture of reactants gives the concentration of the product to be 0.50 M at equilibrium, determine the concentration of the hydrogen.
A) 4.6 x 10–3 M
B) 6.8 x 10–2 M
C) 1.2 x 10–3 M
D) 9.6 x 10–2 M
E) 1.6 x 10–4 M
5) Consider the gaseous reaction CO(g) + Cl2(g) ßà COCl2(g) . What is the expression for Kp in terms of K?
A) K(RT)
B) K/(RT)
C) K(RT)2
D) K/(RT)2
E) 1/K(RT)
6) Consider the gaseous reaction 2NOCl(g) ßà 2NO(g) + Cl2(g) What is the expression for Kp in terms of K?
A) K(RT)
B) K/(RT)
C) K(RT)2
D) K/(RT)2
E) 1/K(RT)
Use the following rxn to answer questions 7&8
2NOBr(g) ßà 2NO(g) + Br2(g)
A 1.0-liter vessel was initially filled with pure NOBr, at a pressure of 4.0 atm, at 300 K.
7) After equilibrium was established, the partial pressure of NOBr was 2.5 atm. What is Kp for the reaction?
A) 0.45
B) 0.27
C) 0.18
D) 0.75
E) none of these
8) After equilibrium was reached, the volume was increased to 2.0 liters, while the temperature was kept at 300 K. This will result in: (equation is on the previous page)
A) an increase in Kp.
B) a decrease in Kp.
C) a shift in the equilibrium position to the right.
D) a shift in the equilibrium position to the left.
E) none of these
9) A sample of solid NH4NO3 was placed in an evacuated container and then heated so that it decomposed explosively according to the following equation: NH4NO3 (s) ßà N2O)g) + 2H2O (g). At equilibrium the total pressure in the container was found to be 3.20 atm at a temperature of 500°C. Calculate Kp.
A) 4.10
B) 1.23
C) 2.56
D) 4.85
E) 1.14
Use the following rxn to answer questions 10-13.
2NOCl(g) ßà 2NO(g) + Cl2(g) with K = 1.6 x 10–5.
1.00 mole of pure NOCl and 1.00 mole of pure Cl2 are placed in a 1.00-L container.
10) If x moles of NOCl react, what is the equilibrium concentration of NO?
A) +x
B) +2x
C) –x
D) –2x
E) x2
11) If x moles of NOCl react, what is the equilibrium concentration of Cl2?
A) +x
B) x/2
C) 1 + x
D) 1 + x/2
E) 1 + 2x
12) Calculate the equilibrium concentration of NO(g).
A) 1.0 M
B) 1.6 x 10–5 M
C) 0.50 M
D) 6.2 x 10–4 M
E) 4.0 x 10–3 M
13) Calculate the equilibrium concentration of Cl2(g).
A) 1.6 x 10–5 M
B) 1.0 M
C) 0.50 M
D) 6.2 x 10–4 M
E) 4.0 x 10–3 M
14) Nitrogen gas (N2) reacts with hydrogen gas (H2) to form ammonia (NH3). At 200°C in a closed container, 1.0 atm of nitrogen gas is mixed with 2.0 atm of hydrogen gas. At equilibrium, the total pressure is 2.0 atm. Calculate the partial pressure of hydrogen gas at equilbrium.
A) 2.0 atm
B) 0.50 atm
C) 1.5 atm
D) 0.0 atm
E) none of these
16) The equilibrium system 2A ßà 2B + C has a very small equilibrium constant: K = 2.6 x 10–6. Initially 3 moles of A are placed in a 1.5-L flask. Determine the concentration of C at equilibrium.
A) 0.011 M
B) 0.022 M
C) 0.033 M
D) 0.044 M
E) 2.0 M
Use the following rxn to answer questions 17-20.
Consider the following equilibrium: 2H2(g) + X2(g) ßà 2H2X(g) + energy
17) Addition of X2 to a system described by the above equilibrium
A) will cause [H2] to decrease.
B) will cause [X2] to decrease.
C) will cause [H2X] to decrease.
D) will have no effect.
E) cannot possibly be carried out.
18) Addition of argon to the above equilibrium
A) will cause [H2] to decrease.
B) will cause [X2] to increase.
C) will cause [H2X] to increase.
D) will have no effect.
E) cannot possibly be carried out.
19) Increasing the pressure by decreasing the volume will cause
A) the reaction to occur to produce H2X.
B) the reaction to occur to produce H2 and X2.
C) the reaction to occur to produce H2 but no more X2.
D) no reaction to occur.
E) X2 to dissociate.
20) Increasing the temperature will cause
A) the reaction to occur to produce H2X.
B) the reaction to occur to produce H2 and X2.
C) the reaction to occur to produce H2 but no more X2.
D) no reaction to occur.
E) an explosion.
21) The value of equilibrium constant K is dependent on
I. the initial concentrations of the reactants.
II. the initial concentrations of the products.
III. the temperature of the system.
IV. the nature of the reactants and products.
A) I, II
B) II, III
C) III, IV
D) It is dependent on three of the above choices.
E) It is not dependent on any of the above choices.
22) Given the following free energies of formation:
DGo
C2H2(g) 209.2 kJ/mol
C2H6(g) –32.9 kJ/mol
calculate Kp at 298 K for C2H2(g) + 2H2(g) C2H6(g)
A) 9.07 ´ 10–1
B) 97.2
C) 1.24 ´ 1031
D) 2.72 ´ 1042
E) None of these is within a factor of 10 of the correct answer.
23) Assume that the reaction CO(g) + H2O(g) ßà CO2(g) + H2(g) occurs in an ideal mixture of ideal gases. At 700 K, Kp = 5.10. At this temperature, DG° equals:
A) 0 kJ
B) 29.7 kJ
C) 9.48 kJ
D) –9.48 kJ
E) –4.12 kJ
24) For the following reaction, CO2(g) + 2H2O(g) ßàCH4(g) + 2O2(g), DH° = 803 kJ
which of the following will increase K?
A) decrease number of moles of methane
B) increase volume of system
C) increase the temperature of system
D) all of these
E) none of these
Use the following rxn to answer questions 25-26
Given CH3CO2H(aq) ßà H+(aq) + CH3CO2–(aq) at 25°C, Ka = 1.8 x 10–5
25) What is DG° at 25°C?
A) –27,000 J
B) +27,000 J
C) –2300 J
D) +2300 J
E) +270 J
26) What is DG at 25°C for a solution in which the concentrations are:
[CH3CO2H] = 0.10 M
[H+] = 2.0 x 10–8 M
[CH3CO2–] = 0.010 M
A) +50. kJ
B) –50. kJ
C) +23 kJ
D) –23 kJ
E) 27 kJ
27) For the reaction CO(g) + 2H2(g) ßà CH3OH(g), DG°700K = –13.46 kJ. The Kp for this reaction at 700. K is:
A) 10.1
B) 16.7
C) 22.5
D) 9.90 x 10–2
28) Water gas, a commercial fuel, is made by the reaction of hot coke carbon with steam.
C(s) + H2O(g) ßà CO(g) + H2(g)
When equilibrium is established at 800°C the concentrations of CO, H2, and H2O
are 4.00 x 10–2, 4.00 x 10–2, and 1.00 x 10–2 mole/liter, respectively. Calculate the value of DG° for this reaction at 800°C.
A) 109 kJ
B) –43.5 kJ
C) 193 kJ
D) 16.3 kJ
E) none of these
29) Does the reaction above favor products or reactants? Explain.
1)a, 2)c 3)a 4)b 5)b 6)a 7)b 8)c 9)d 10)a 11)d 12)e 13)b 14)b 16)a 17)a 18)d 19)a 20)b 21)c 22)d 23)d 24)c 25)b 26)a 27)a 28)d