Equilibrium

2 SO2(g) + O2(g) ⇄ 2 SO3(g) When 0.40 moles of SO2 and 0.60 moles of O2 are placed in an evacuated 1.00-liter flask, the reaction represented above occurs. After the reactants and the product reach equilibrium and the initial temperature is restored, the flask is found to contain 0.30 moles of SO3. Based on these results, the expression for the equilibrium constant, Kc, of the reaction is... (A) (0.30)2 / [(0.65)(0.10)2] (B) (0.30)2 / [(0.60)(0.40)2] (C) (2 x 0.30) / [(0.45)(2 x 0.10)] (D) (0.30) / [(0.65)(0.10)] (E) (0.30) / [(0.60)(0.40)]

A

Appropriate uses of a visible-light spectrophotometer include which of the following? I. Determining the concentration of a solution of Cu(NO3)2 II. Measuring the conductivity of a solution of KMnO4 III. Determining which ions are present in a solution that may contain Na+, Mg2+, Al3+ (A) I only (B) II only (C) III only (D) I and II only (E) I and III only

A

HCO3−(aq) + OH− (aq) ⇄ H2O(l) + CO32− (aq) ΔH° = −41.4kJ When the reaction represented by the equation above is at equilibrium at 1 atm and 25°C, the ratio [CO32−] can be increased by doing which of the following? [HCO3−] (A) Decreasing the temperature (B) Adding acid (C) Adding a catalyst (D) Diluting the solution with distilled water (E) Bubbling neon gas through the solution

A

In a saturated solution of Zn(OH)2 at 25°C , the value of [OH−] is 2.0 × 10−6M. What is the value of the solubility-product constant, Ksp, for Zn(OH)2 at 25°C ? (A) 4.0 × 10−18 (B) 8.0 × 10−18 (C) 1.6 × 10−17 (D) 4.0 × 10−12 (E) 2.0 × 10−6

A

PCl3(g) + Cl2(g) ⇄ PCl5(g) + energy Some PCl3 and Cl2 are mixed in a container at 200 °C and the system reaches equilibrium according to the equation above. Which of the following causes an increase in the number of moles of PCl5 present at equilibrium? I. Decreasing the volume of the container II. Raising the temperature III. Adding a mole of He gas at constant volume (A) I only (B) II only (C) I and III only (D) II and III only (E) I, II, and III

A

2NO(g) + O2(g) ⇄ 2 NO2(g) ; ∆H < 0 Which of the following changes alone would cause a decrease in the value of Keq for the reaction represented above? (A) Decreasing the temperature (B) Increasing the temperature (C) Decreasing the volume of the reaction vessel (D) Increasing the volume of the reaction vessel (E) Adding a catalyst

B

For the reaction A(g) ⇄ B(g) + C(g), the equilibrium constant, Kp, is 2 x 10−4 at 25 °C. A mixture of the three gases at 25 °C is placed in a reaction flask and the initial pressures are PA = 2 atm, PB = 0.5 atm, and PC = 1 atm. At the instant of mixing, which of the following is true for the reaction as written? (A) ∆G < 0 (B) ∆G > 0 (C) ∆S = 0 (D) ∆G° = 0 (E) ∆G° < 0

B

H2(g) + Br2(g) ⇄ 2HBr(g) At a certain temperature, the value of the equilibrium constant, K, for the reaction represented above is 2.0 × 105. What is the value of K for the reverse reaction at the same temperature? (A) −2.0 × 10−5 (B) 5.0 × 10−6 (C) 2.0 × 10−5 (D) 5.0 × 10−5 (E) 5.0 × 10−4

B

HgO(s) + 4 I− + H2O ⇄ HgI42− + 2 OH−; ∆H < 0 Consider the equilibrium above. Which of the following changes will increase the concentration of HgI42−? (A) Increasing the concentration of OH− (B) Adding 6 M HNO3 (C) Increasing the mass of HgO present (D) Increasing the temperature (E) Adding a catalyst

B

CuO(s) + H2(g) ⇄ Cu(s) + H2O(g) ; ∆H = − 2.0 kilojoules When the substances in the equation above are at equilibrium at pressure P and temperature T, the equilibrium can be shifted to favor the products by... (A) increasing the pressure by means of a moving piston at constant T. (B) increasing the pressure by adding an inert gas such as nitrogen. (C) decreasing the temperature. (D) allowing some gases to escape at constant P and T. (E) adding a catalyst.

C

The solubility of CuI is 2 x 10−6 molar. What is the solubility product constant, Ksp, for CuI? (A) 1.4 x 10−3 (B) 2 x 10−6 (C) 4 x 10−12 (D) 2 x 10−12 (E) 8 x 10−18

C

4 HCl(g) + O2(g) ⇄ 2 Cl2(g) + 2 H2O(g) Equal numbers of moles of HCl and O2 in a closed system are allowed to reach equilibrium as represented by the equation above. Which of the following must be true at equilibrium? I. [HCl] must be less than [Cl2]. II. [O2] must be greater than [HCl]. III. [Cl2] must equal [H2O]. (A) I only (B) II only (C) I and III only (D) II and III only (E) I, II, and III

D

How many moles of NaF must be dissolved in 1.00 liter of a saturated solution of PbF2 at 25 °C to reduce the [Pb2+] to 1 x 10−6 molar? (Ksp of PbF2 at 25 °C = 4.0 x 10−8) (A) 0.020 mole (B) 0.040 mole (C) 0.10 mole (D) 0.20 mole (E) 0.40 mole

D

MnS(s) + 2 H+ ⇄ Mn2+ + H2S(g) At 25 °C the solubility product constant, Ksp, for MnS in 5 x 10−15 and the acid dissociation constants K1 and K2 for H2S are 1 x 10−7 and 1 x 10−13, respectively. What is the equilibrium constant for the reaction represented by the equation above at 25 °C? (A) 1 x 10−13 / 5 x 10−15 (B) 5 x 10−15 / 1 x 10−7 (C) 1 x 10−7 / 5 x 10−20 (D) 5 x 10−15 / 1 x 10−20 (E) 1 x 10−20 / 5 x 10−15

D

2 SO3(g) ⇄ 2 SO2(g) + O2(g) After the equilibrium represented above is established, some pure O2(g) is injected into the reaction vessel at constant temperature. After equilibrium is reestablished, which of the following has a lower value compared to its value at the original equilibrium? (A) Keq for the reaction (B) The total pressure in the reaction vessel (C) The amount of SO3(g) in the reaction vessel (D) The amount of O2(g) in the reaction vessel (E) The amount of SO2(g) in the reaction vessel

E

In which of the following systems would the number of moles of the substances present at equilibrium NOT be shifted by a change in the volume of the system at constant temperature? (A) CO(g) + NO(g) ⇄ CO2(g) + 1/2 N2(g) (B) N2(g) + 3 H2(g) ⇄ 2 NH3(g) (C) N2(g) + 2 O2(g) ⇄ 2 NO2(g) (D) N2O4(g) ⇄ 2 NO2(g) (E) NO(g) + O3(g) ⇄ NO2(g) + O2(g)

E

The test for the presence of Ag+ in an unknown solution involves the treatment of the silver-ammonia complex with dilute hydrochloric acid. The appearance of a white precipitate at this point indicates the presence of silver ion in the original sample. The net ionic equation that represents this test is... (A) Ag(NH4)4+ + 4 H+ ⇄ Ag(s) + 4 NH4+ (B) Ag(NH4)4+ + Cl− ⇄ AgCl(s) + 4 NH4+ (C) Ag(NH3)4+ + 4 HCl ⇄ AgCl(s) + 4 NH4+ + 3 Cl− (D) Ag(NH3)4+ + Cl− ⇄ Ag(NH3)2Cl(s) (E) Ag(NH3)4+ + 2 H+ + Cl− ⇄ AgCl(s) + 2 NH4+

E