Chemistry : True or False type question on Chemical Equilibrium

1. If equilibrium constant for the reaction A2 + B2 ↔ 2AB, is K, then for the backward reaction AB ↔ ½ A2 + ½ B2, the equilibrium constant is 1/K. (JEE 1984)

Answer: False

Reason: For A2 + B2 ↔ 2AB,
K = [AB] ²/[A2][B2]

For AB ↔ ½ A2 + ½ B2 equilibrium constant is

= [A2] ^1/2[B2] ^1/2/[AB]

This is not equal to 1/K.

2. Solubility of sodium hydroxide increases with increase in temperature. (JEE 1985).
Answer: False

3. From the solution containing copper (+2) and zinc (+2) ions , copper can be selectively precipitated using sodium sulphide. (JEE 1987)

False

Na2S will produce an alkaline solution, both copper (+2) and zinc (+2) ions would be precipitated.

4. The rate of exothermic reaction increases with increasing temperature. (JEE 1990).

Answer: True
Reason: In general, rate of a reaction increases with increase in temperature which is due to increase in the rate constant of the reaction. As per the Arrhenius equation relating k and T, as temperature increases k increases. (Note: At equilibrium if the temperature is increased, for an exothermic reaction the equilibrium shifts leftward).