# MCQ | Chemical Equilibrium

QUIZ – I

Q:1. When KOH is dissolved in water, heat is evolved. If the temperature is raised, the solubility of KOH.

(A) Increases

(B) Decreases

(C) Remains the same

(D) Cannot be predicted

Ans: (B)

Q:2. For the liquefaction of gas, the favourable conditions are

(A) Low T and high P

(B) Low T and low P

(C) Low T and high P and a catalyst

(D) Low T and catalyst

Ans: (A)

Q:3. Consider the water gas equilibrium reaction

C(s) + H2O(g)  $\rightleftharpoons$ CO(g) + H2(g)

Which of the following statement is true at equilibrium

(A) If the amount of C(s) is increased, less water would be formed

(B) If the amount of C(s) is increased, more CO and H2 would be formed

(C) If the pressure on the system is increased by halving the volume, more water would be formed.

(D) If the pressure on the system is increased by halving the volume, more CO and H2 would be formed.

Ans: (C)

Q:4. A reaction takes place in two steps with equilibrium constants 10–2 for slow step and 102 for last step. The equilibrium constant of the overall reaction will be

(A) 104

(B) 10—4

(C) 1

(D) 10–2

Ans: (C)

Q:5. For the reaction PCl3(g) + Cl2(g) $\rightleftharpoons$ PCl5(g), the value of KC at 250°C is 26 mol–1/litre. The value of Kp at this temperature will be

(A) 0.61 atm–1

(B) 0.57 atm–1

(C) 0.85 atm–1

(D) 0.46 atm–1

Ans: (A)

Q:6. According to Le Chatlier’s principle adding heat to a solid and liquid in equilibrium with endothermic nature will cause the

(A) Amount of solid to decrease

(B) Amount of liquid to decrease

(C) Temperature to rise

(D) Temperature to fall

Ans: (A)

Q:7. An aqueous solution of hydrogen sulphide shows the equilibrium

H2S $\rightleftharpoons$ H+ + HS

If dilute hydrochloric acid is added to an aqueous  solution of H2S, without any change in temperature, then

(A) The equilibrium constant will change

(B) The concentration of HS will increase

(C) The concentration of undissociated hydrogen sulphide will decrease

(D) The concentration of HS will decrease

Ans: (D)

Q:8. What would happen to a reversible reaction at equilibrium when temperature is raised, given that its DH is positive

(A) More of the products are formed

(B) Less of the products are formed

(C) More of the reactants are formed

(D) It remains in equilibrium

Ans: (A)

Q:9. Applying the law of mass action to the dissociation of hydrogen Iodide

2HI(g) $\rightleftharpoons$  H2 + I2

We get the following expression

$\frac{(a-x)(b-x)}{4 x^2} = K$

Where a is original concentration of H2, b is original concentration of I2, x is the number of molecules of H2 and I2 reacted with each other. If the pressure is increased in such a reaction then

(A) $K = \frac{(a-x)(b-x)}{4 x^2}$

(B) $K > \frac{(a-x)(b-x)}{4 x^2}$

(C) $K < \frac{(a-x)(b-x)}{4 x^2}$

(D) none of these

Ans: (A)

Q:10. One mole of ethanol is treated with one mole of ethanoic acid at 25°C.
One–fourth of the acid changes into ester at equilibrium. The equilibrium constant for the reaction will be

(A) 1/9

(B) 4/9

(C) 9

(D) 9/4

Ans: (A)

Q:11. The equilibrium, PCl5(g) $\rightleftharpoons$ PCl3(g) + Cl2(g) is attained at 25°C in a closed container and an inert gas He is introduced. Which of the following statements are correct.

(A) concentration of PCl5, PCl3 and Cl2 are changed

(B) more Cl­2 is formed

(C) concentration of PCl3 is reduced

(D) Nothing happens

Ans: (D)

Q:12. In which of the following equilibrium, the value of KP is less than KC?

(A) N2O4 $\rightleftharpoons$ 2NO2

(B) N2 + O2 $\rightleftharpoons$ 2NO

(C) N2 + 3H2 $\rightleftharpoons$ 2NH3

(D) 2SO2 + O2 $\rightleftharpoons$  2SO3

Ans: (C)

Q:13. In the reaction A2(g) + 4B2 (g) $\rightleftharpoons$ 2AB4(g) , ΔH > 0. The decomposition of AB4 (g) will be favoured at

(A) low temperature and high pressure

(B) high temperature and low pressure

(C) low temperature and low pressure

(D) high temperature and high pressure

Ans: (C)

Q:14. For the reaction, 2NO2 (g) $\rightleftharpoons$ 2NO(g) + O2 (g), KC = 1.8 ×10–6 at 185°C. At 185°C,  the value of KC for the reaction:

NO(g) + (1/2)O2 (g) $\rightleftharpoons$ NO2 (g) is

(A) 0.9 × 106

(B) 7.5 ×102

(C) 1.95 ×10–3

(D) 1.95 ×103

Ans: (B)

Q:15. For the gaseous phase reaction, 2A $\rightleftharpoons$ B + C,  ΔH° = –40 Kcal mol–1 which statement is correct for

(A) K is independent of temperature

(B) K increase as temperature decrease

(C) K increase as temperature increases

(D) K varies with addition of A

Ans: (C)

Q:16. On applying pressure to the equilibrium

$\large ice \rightleftharpoons water$

Which phenomenon will happen

(A) More ice will be formed

(B) More water will be formed

(C) Equilibrium will not be disturbed

(D) Water will evaporate

Ans: (B)

Q:17. Densities of diamond and graphite are 3.5 and 2.3 grams respectively. Increase of pressure on the equilibrium

Cdiamond $\rightleftharpoons$ Cgraphite

(A) Favours backward reaction

(B) Favours forward reaction

(C) Have no effect

(D) Increase the reaction rate

Ans: (A)

Q:18. For the reaction N2 + 3H2 $\rightleftharpoons$ 2NH3 in a vessel after the addition of equal number of mole of N2 and H2 equilibrium state is formed which of the following is correct ?

(A) [H2] = [N2]

(B) [H2] < [H2]

(C) [H2] > [N2]

(D) [H2] > [NH3]

Ans: (B)

Q:19. One mole of N­2O4(g) at 300 K is kept in a closed container under one atm. It is heated to 600 K when 20% by mass of N2O4(g) decomposes to NO2(g). The resultant pressure is

(A) 1.2 atm

(B) 2.4 atm

(C) 2.0 atm

(D) 1.0 atm

Ans: (B)

Q:20. At 30°C, Kp for the dissociation reaction

SO2(g) $\rightleftharpoons$ SO2(g) + Cl2(g)

is 2.9 × 10–2 atm. If the total pressure is 1 atm, the degree of dissociation of SO2Cl2 is

(A) 87%

(B) 13%

(C) 17%

(D) 29%

Ans: (C)

Q:21. A vessel at 1000K contains CO2 with a pressure of 0.5 atm. Some of the CO2 is converted into CO on the addition of graphite. The value of K if the total pressure at equilibrium is 0.8 atm is

(A) 1.8 atm

(B) 3 atm

(C) 0.3 atm

(D) 0.18 atm

Ans: (A)

Q:22. Vapour density of PCl5 is 104.16 but when heated at 230°C its vapour density is reduced to 62. The degree of dissociation of PCl5 at this temperature will be

(A) 6.8%

(B) 68%

(C) 46%

(D) 64%

Ans: (B)

Q:23. For the reaction SO2(g) + (1/2)O2(g) $\rightleftharpoons$ SO3(g) Kp = 1.7 × 1012 at 20°C and 1 atm pressure. Calculate Kc.

(A) 1.7 × 1012

(B) 0.7 × 1012

(C) 8.33 × 1012

(D) 1.2 × 1012

Ans: (C)

Q:24. For a gaseous equilibrium

2A(g) $\rightleftharpoons$ 2B(g) + C(g) , Kp has a value 1.8 at 700°K. What is the value of Kc for the equilibrium

2B(g) + C(g) $\rightleftharpoons$ 2A at that temperature

(A) ≈ 0.031

(B) ≈ 32

(C) ≈ 44.4

(D) ≈ 1.3  × 10–3

Ans: (C)

Q:25. For the reaction N2O4(g) $\rightleftharpoons$ 2NO2(g) the reaction connecting the degree of dissociation (α) of N2O4(g) with its equilibrium constant KP is

(A) $\alpha = \frac{K_P/P}{4 + K_P/P}$

(B) $\alpha = \frac{K_P}{4 + K_P}$

(C) $\alpha = [\frac{K_P/P}{4 + K_P/P} ]^{1/2}$

(D) $\alpha = [ \frac{K_P}{4 + K_P} ]^{1/2}$

Ans: (C)

Q:26. In a closed container at 1 atm pressure 2 moles of SO2(g) and 1 mole of O2(g) were allowed to react to form SO3(g) under the influence of acetalyst. Reaction 2SO2(g) + O2(g) $\rightleftharpoons$ 2SO3(g) occurred

At equilibrium it was found that 50% of SO2(g) was converted to SO3(g). The formal pressure of O­2 (g) at equilibrium will be

(A) 0.66 atm

(B) 0.493 atm

(C) 0.33 atm

(D)  0.20 atm

Ans: (D)

Q:27. KP for a reaction at 25°C is 10 atm. The activation energy for forward and reverse reactions are 12 and 20 kJ / mol respectively. The KC for the reaction at 40°C will be

(A) 4.33 ×10–1 M

(B ) 3.33 ×10–2 M

(C) 3.33 ×10–1 M

(D) 4.33 ×10–2 M

Ans: (C)

Q:28. K for the synthesis of HI (g) is 50. The degree of dissociation of HI is

(A) 0.10

(B) 0.14

(C) 0.18

(D) 0.22

Ans: (D)

Q:29. One mole of N2O4(g) at 300 K is kept in a closed container under one atmosphere. It is heated to 600 K when N2O4 (g) decomposes to NO2(g). If the resultant pressure is 2.4 atm, the percentage dissociation by mass of N2O4 (g) is

(A) 10%

(B) 20%

(C) 30%

(D) 40%

Ans: (B)

Q:30. 40% of a mixture of 0.2 mol of N2 and 0.6 mol of H2 react to give NH3 according to the equation:

N2(g) + 3H2(g) $\rightleftharpoons$  2NH3(g) at constant  temperature  and pressure. Then the ratio of the final volume to the initial volume of gases are

(a) 4:5

(b) 5:4

(C) 7:10

(D) 8:5