NEET Equilibrium — Set 9

Question 1

In a closed container, the vapor pressure of a liquid reaches a constant value at a fixed temperature. What does this indicate?

Accepted Answer

The constant vapor pressure indicates that the rate of evaporation equals the rate of condensation, establishing a dynamic equilibrium between the liquid and its vapor.

Question 2

A weak acid $ \ce{HA} $ ($ K_a = 1.6 \times 10^{-6} $) is mixed with 0.05 M $ \ce{NaA} $ and 0.1 M $ \ce{HCl} $ in equal volumes. What is the pH?

Accepted Answer

After mixing: $ [\ce{HCl}] = 0.05 \, \text{M} $, $ [\ce{A-}] = 0.025 \, \text{M} $, $ [\ce{HA}] $ negligible due to common ion effect. $ K_a = \frac{[\ce{H+}][\ce{A-}]}{[\ce{HA}]} $, $ [\ce{H+}] \approx 0.05 $, $ \text{pH} = -\log(0.05) = 1.3 $.

Question 3

For $ \ce{A(g) <=> 2B(g)} $, $ K_c = 0.25 $ at 500 K. If 0.4 mol $ \ce{A} $ is in a 1 L vessel, what is $ [\ce{B}] $ at equilibrium?

Accepted Answer

Initial: $ [\ce{A}] = 0.4 \, \text{M} $, $ [\ce{B}] = 0 $. Let $ 2x = [\ce{B}] $, $ [\ce{A}] = 0.4 - x $. $ K_c = \frac{[\ce{B}]^2}{[\ce{A}]} = \frac{(2x)^2}{0.4 - x} = 0.25 $, $ 4x^2 = 0.1 - 0.25x $, $ x \approx 0.125 $, $ [\ce{B}] = 0.25 \, \text{M} $.

NEET Chemistry: Equilibrium — Practice Set 9

Q1. In a closed container, the vapor pressure of a liquid reaches a constant value at a fixed temperature. What does this indicate?

Q2. A weak acid \( \ce{HA} \) (\( K_a = 1.6 \times 10^{-6} \)) is mixed with 0.05 M \( \ce{NaA} \) and 0.1 M \( \ce{HCl} \) in equal volumes. What is the pH?

Q3. For \( \ce{A(g) <=> 2B(g)} \), \( K_c = 0.25 \) at 500 K. If 0.4 mol \( \ce{A} \) is in a 1 L vessel, what is \( [\ce{B}] \) at equilibrium?

Q4. For \( \ce{AB(s) <=> A+(aq) + B-(aq)} \), if \( K_{sp} = 4.0 \times 10^{-8} \), what is \( [\ce{B-}] \) in mol/L?

Q5. In the equilibrium \( \ce{2P(g) <=> Q(g) + R(g)} \), adding \( \ce{Q} \) at constant volume will shift the equilibrium in which direction?

Q6. For \( \ce{2NOCl(g) <=> 2NO(g) + Cl2(g)} \), \( K_p = 1.8 \times 10^{-2} \) at 500 K. If 2 moles of \( \ce{NOCl} \) are placed in a 2 L vessel, what is the total pressure at equilibrium (\( R = 0.0831 \, \text{bar L/mol K} \))?

Q7. A weak acid \( \ce{HY} \) (\( K_a = 2.0 \times 10^{-5} \)) is mixed with 0.01 M \( \ce{NaOH} \) in a 2:1 volume ratio (acid:base). If the final \( [\ce{HY}] = 0.04 \, \text{M} \), what is the pH?

Q8. A weak base \( \ce{BOH} \) (\( K_b = 2.5 \times 10^{-5} \)) has a 0.1 M solution with \( \alpha = 0.005 \). What is the pH?

Q9. For \( \ce{CO(g) + 2H2(g) <=> CH3OH(g)} \), \( K_c = 10 \) at 600 K. If 0.2 mol \( \ce{CO} \) and 0.4 mol \( \ce{H2} \) are in a 1 L vessel, what is \( [\ce{CH3OH}] \) at equilibrium?

Q10. The \( K_w \) of water at 310 K is \( 2.9 \times 10^{-14} \). What is the pH of pure water at this temperature?