Chemical Equilibrium(12th Grade > Chemistry ) Questions and answers for exam Preparation

12th Grade > Chemistry

CHEMICAL EQUILIBRIUM MCQs

Total Questions : 30 | Page 2 of 3 pages

Question 11. Hl was heated in a closed tube at

440^{\circ} c

till equilibrium is obtained. At this temperature

22 %

of Hl was dissociated. The equilibrium constant for this dissociation will be

0.282
0.0796
0.0199
1.99

Discuss Question

Answer: Option C. -> 0.0199
:
C

2 H I ⇋ H_{2} + l_{2}

\begin{matrix} I n i t i a l n o o f m o l e s - & 2 m o l e s & 0 & 0 a t e q u i l i b r i u m & 2 m o l e s - 0.44 & 0.22 & 0.22 \end{matrix}

K_{c} = \frac{[H_{2}] [l_{2}]}{[H I]^{2}} = \frac{0.22 \times 0.22}{{1.56}^{2}} = 0.0199

Question 12. When hydrochloric acid is added to cobalt nitrate solution at room temperature, the following reaction takes place and the reaction mixture becomes blue. On cooling the mixture it becomes pink. On the basis of this information mark the correct answer.

[C o (H_{2} O)_{6}]^{3^{+}} (a q)      p i n k + 4 C l^{-} (a q) ⇋ [C_{o} C l_{4}]^{2^{-}} (a q)      b l u e + 6 H_{2} O (l)

△ H> o for the reaction
△ H
△ H= o for the reaction
The sign of △ H canot be predicted on the basis of this information

Discuss Question

Answer: Option A. -> △ H> o for the reaction
:
A
On cooling the reaction is moving in backward direction.Thus backward reaction is exothermic.
Hence forward reaction is endothermic~i.e.

△ H > o .

Question 13. Chemical equilibrium is dynamic in nature because

Equilibrium is maintained rapidly
The concentration of reactants and products become same at equilibrium
The concentration of reactants and products are constant but different
Both forward and backward reactions occur at all times with same speed

Discuss Question

Answer: Option D. -> Both forward and backward reactions occur at all times with same speed
:
D
Chemical equilibrium is dynamic in nature because, reactants change into products and products change into reactants even after equilibrium is achieved. But rate of forward and backward reactions are same.

Question 14. Which of the followings is incorrect?

According to law of mass action, rate of a chemical reaction is proportional to molar concentration of reactants.
If Kc › 1 then products are present predominantly at equilibrium.
Catalysts increase the rate of forward reaction as well as backward reaction.
Value of equilibrium constant increases with increase in temperature.

Discuss Question

Answer: Option D. -> Value of equilibrium constant increases with increase in temperature.
:
D
a) According to law of mass action,rate of a chemical reaction is proportional to molar concentration of reactants.

b) At equilibrium,

Products are present predominantly if $K_{c} > 1$

Products are present predominantly if $K_{c} < 1$

b) Though value of equilibrium constant doest not charge, catalysts increase the rate of both the forward and backward reactions.
c)

l n \frac{k_{2}}{k_{1}} = \frac{△ H}{R} (\frac{1}{T_{1}} - \frac{1}{T_{2}})

I f T_{2} > T_{1},

$K_{2} < K_{1} i f △ H > 0$ i.e. reaction is endothermic

$K_{2} < K_{1} i f △ H > 0$ i.e. reaction is exothermic

Hence this Optionis incorrect

Question 15. At a temperature of

1000 K

, equilibrium constant

K_{c}

for the following reaction is

100 m o l^{2} L^{- 2}

N_{2} (g) + 3 H_{2} (g) ⇋ 2 N H_{3} (g)

What will be the value of

K_{p}

for the reaction below?

N H_{3} (g) ⇋ \frac{1}{2} N_{2} (g) + \frac{3}{2} H_{2} (g)

0.1 atm
8.21 atm
831.4 atm
8.314 atm

Discuss Question

Answer: Option B. -> 8.21 atm
:
B

N H_{3} (g) ⇋ \frac{1}{2} N_{2} (g) + \frac{3}{2} H_{2} (g) K_{c} = K_{c}^{'}

K_{c}^{'} = (\frac{1}{100})^{\frac{1}{2}} = 0.1

K_{p} = K_{c}^{'} \times (R T)^{△ n} = 0.1 \times (0.0821 \times 1000)^{1} = 8.21 a t m

Notes: Use

R = 0.0821 a t m l m o l^{- 1} K^{- 1}

as unit of concentration has been taken as

m o l / l

while calculating

K_{c} .

Question 16. The reaction quotient (Q) for a reaction is given as

Q = \frac{[N H_{3}]^{2}}{[N_{2}] [H_{2}]^{3}}

. The reaction will proceed from left to right if ........

Q=0
Q> kc
Q
Q=kc

Discuss Question

Answer: Option C. -> Q
:
C
Reaction moves in forward direction if

Q < K_{c}

Reaction moves in backward direction if

Q > K_{c}

Reaction remains at equilibrium if

Q = K_{c}

Question 17. At equilibrium, reaction $A ⇋ B$ is at the stage of half completion. Which one of the followings is true?

△ G∘=0
△ G∘>0
△ G∘
△ G∘ = −RTln2

Discuss Question

Answer: Option A. -> △ G∘=0
:
A
At the stage of half completion of the reaction

[A] = [B]

K_{e q} = \frac{[B]}{[A]} = 1

△ G^{\circ} = - R T l n k_{e q} = 0

Question 18. When a bottle of cold drink is opened, the gas comes out with a fizze due to -

Decrease in temperature
Increase in pressure
Decrease in pressure suddenly which results in decrease of solubility of CO2 gas in water
None of these

Discuss Question

Answer: Option C. -> Decrease in pressure suddenly which results in decrease of solubility of CO2 gas in water
:
C
Solubility of gas in liquid decrease with decrease in its partial pressure

Question 19. 1 mole of