Law of chemical equilibrium; Kp and Kc — practice questions

Question 1 · difficulty L2 · understanding

One mole each of He and $\mathrm{A}(\mathrm{g})$ are taken in a 10 L closed flask and heated to 400 K to establish the following equilibrium. $$\mathrm{A}(\mathrm{~g}) \rightleftharpoons \mathrm{B}(\mathrm{~g})$$ $\mathrm{K}_{\mathrm{c}}$ for this reaction at 400 K is 4.0 . The partial pressures (in atm) of He and B(g) are respectively (at equilibrium) (Assume $\mathrm{He}, \mathrm{A}(\mathrm{g})$ and $\mathrm{B}(\mathrm{g})$ behave as ideal gases) (Given : $\mathrm{R}=0.082 \mathrm{~L} \mathrm{~atm} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}$ )

• A. 3.28, 2.624
• B. 2.624, 3.28
• C. 3.28, 0.656
• D. 0.656, 6.56

Question 2 · difficulty L2 · understanding

At $\mathrm{T}(\mathrm{K})$, the equilibrium constant of $\mathrm{A}_2(g)+\mathrm{B}_2(g) \rightleftharpoons \mathrm{C}(g)$ is $2.7 \times 10^{-5}$. What is the equilibrium constant for $\frac{1}{3} \mathrm{~A}_2(\mathrm{~g})+\frac{1}{3} \mathrm{~B}_2(\mathrm{~g}) \rightleftharpoons \frac{1}{3} \mathrm{C}(\mathrm{g})$ at the same temperature?

• A. $\left(2.7 \times 10^{-5}\right)^3$
• B. $6 \times 10^{-2}$
• C. $\sqrt{2.7 \times 10^{-5}}$
• D. $3\times 10^{-2}$

Question 3 · difficulty L2 · understanding

Given below are two statements : Statement I : A catalyst cannot alter the equilibrium constant $\left(\mathrm{K}_{\mathrm{c}}\right)$ of the reaction, temperature remaining constant. Statement II : A homogenous catalyst can change the equilibrium composition of a system, temperature remaining constant. In the light of the above statements, choose the correct answer from the options given below

• A. Statement I is true but Statement II is false
• B. Statement I is false but Statement II is true
• C. Both Statement I and Statement II are true
• D. Both Statement I and Statement II are false

Question 4 · difficulty L2 · understanding

A vessel at 1000 K contains $\mathrm{CO}_2$ with a pressure of 0.5 atm . Some of $\mathrm{CO}_2$ is converted into CO on addition of graphite. If total pressure at equilibrium is 0.8 atm , then K p is :

• A. 0.18 atm
• B. 0.3 atm
• C. 3 atm
• D. 1.8 atm

Question 5 · difficulty L2 · understanding

For the given hypothetical reactions, the equilibrium constants are as follows : $$\begin{aligned} & \mathrm{X} \rightleftharpoons \mathrm{Y} ; \mathrm{K}_1=1.0 \\ & \mathrm{Y} \rightleftharpoons \mathrm{Z} ; \mathrm{K}_2=2.0 \\ & \mathrm{Z} \rightleftharpoons \mathrm{W} ; \mathrm{K}_3=4.0 \end{aligned}$$ The equilibrium constant for the reaction $$\mathrm{X} \rightleftharpoons \mathrm{W}$$ is

• A. 12.0
• B. 8.0
• C. 6.0
• D. 7.0

Question 6 · difficulty L2 · understanding

The ratio $$\frac{K_P}{K_C}$$ for the reaction : $$\mathrm{CO}_{(\mathrm{g})}+\frac{1}{2} \mathrm{O}_{2(\mathrm{~g})} \rightleftharpoons \mathrm{CO}_{2(\mathrm{~g})}$$ is :

• A. 1
• B. $$(\mathrm{RT})^{1 / 2}$$
• C. RT
• D. $$\mathrm{ \frac{1}{\sqrt{R T}}}$$

Question 7 · difficulty L2 · understanding

At $$-20^{\circ} \mathrm{C}$$ and $$1 \mathrm{~atm}$$ pressure, a cylinder is filled with equal number of $$\mathrm{H}_2, \mathrm{I}_2$$ and $$\mathrm{HI}$$ molecules for the reaction $$\mathrm{H}_2(\mathrm{~g})+\mathrm{I}_2(\mathrm{~g}) \rightleftharpoons 2 \mathrm{HI}(\mathrm{g})$$, the $$\mathrm{K}_{\mathrm{p}}$$ for the process is $$x \times 10^{-1}$$. $$\mathrm{x}=$$ __________. [Given : $$\mathrm{R}=0.082 \mathrm{~L} \mathrm{~atm} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}$$]

• A. 2
• B. 1
• C. 10
• D. 0.01

Question 8 · difficulty L2 · understanding

The equilibrium constant for the reaction $$\mathrm{SO}_3(\mathrm{~g}) \rightleftharpoons \mathrm{SO}_2(\mathrm{~g})+\frac{1}{2} \mathrm{O}_2(\mathrm{~g})$$ is $$\mathrm{K}_{\mathrm{c}}=4.9 \times 10^{-2}$$. The value of $$\mathrm{K}_{\mathrm{c}}$$ for the reaction given below is $$2 \mathrm{SO}_2(\mathrm{~g})+\mathrm{O}_2(\mathrm{~g}) \rightleftharpoons 2 \mathrm{SO}_3(\mathrm{~g})$$ is :

• A. 49
• B. 416
• C. 41.6
• D. 4.9

Question 9 · difficulty L2 · understanding

For the given reaction, choose the correct expression of $$\mathrm{K}_{\mathrm{C}}$$ from the following :- $$\mathrm{Fe}_{(\mathrm{aq})}^{3+}+\mathrm{SCN}_{(\mathrm{aq})}^{-} \rightleftharpoons(\mathrm{FeSCN})_{(\mathrm{aq})}^{2+}$$

• A. $$\mathrm{K}_{\mathrm{C}}=\frac{\left[\mathrm{Fe}^{3+}\right]\left[\mathrm{SCN}^{-}\right]}{\left[\mathrm{FeSCN}^{2+}\right]}$$
• B. $$\mathrm{K}_{\mathrm{C}}=\frac{\left[\mathrm{FeSCN}^{2+}\right]}{\left[\mathrm{Fe}^{3+}\right]\left[\mathrm{SCN}^{-}\right]}$$
• C. $$\mathrm{K}_{\mathrm{C}}=\frac{\left[\mathrm{FeSCN}^{2+}\right]^2}{\left[\mathrm{Fe}^{3+}\right]\left[\mathrm{SCN}^{-}\right]}$$
• D. $$\mathrm{K}_{\mathrm{C}}=\frac{\left[\mathrm{FeSCN}^{2+}\right]}{\left[\mathrm{Fe}^{3+}\right]^2\left[\mathrm{SCN}^{-}\right]^2}$$

Question 10 · difficulty L2 · understanding

The equilibrium constant for the reversible reaction 2A(g) $$\rightleftharpoons$$ 2B(g) + C(g) is K 1 $${3 \over 2}$$A(g) $$\rightleftharpoons$$ $${3 \over 2}$$B(g) + $${3 \over 4}$$C(g) is K 2 . K 1 and K 2 are related as :

• A. $${K_1} = \sqrt {{K_2}}$$
• B. $${K_2} = \sqrt {{K_1}}$$
• C. $${K_2} = K_1^{3/4}$$
• D. $${K_1} = K_2^{3/4}$$