Question

Consider this gas phase equilibrium system:

PCl5(g) equilibrium arrow PCl3(g) + Cl2

deltaH = +87.8 kJ/mol

Which of these statements are false?

A) increasing the temperature causes the equilibrium constant to increase

B) increasing the system volume shifts the equilibrium to the right

C) increasing the temperature shifts the equilibrium to the right

D) a catalyst speeds up the approach to equilibrium and shifts the position from equilibrium to the right.

E) decreasing the total pressure of the system shifts the equilibrium to the right.

Answer 1

Ans: false statement = d

PCl5 (g) <----------> PCl3 (g) + Cl2 (g)   deltaH = +87.8 kJ/mol

delta n = moles of products - moles of reactants = 2 -1 = 1

deltaH = +ve

This is endothermic reaction.

a) true

Explanation :

Endothermic reactions are favoured by increase in temperature.

So, forward reaction is favoured. Hence more products will be formed.

So, equilibrium constant will be increased.

b) true

delta n = moles of products - moles of reactants = 2 -1 = 1

delta n = +ve

Forward reaction favours more volume.

Hence,

increasing the system volume shifts the equilibrium to the right

c) true

Endothermic reactions are favoured by increase in temperature.

Hence,  increasing the temperature shifts the equilibrium to the right.

d) False

Catalyst do not alter the position of equilibrium . Catalyst helps to attain the equilibrium quickly.

e) true

delta n = moles of products - moles of reactants = 2 -1 = 1

delta n = +ve

Forward reaction favours low pressure.

Hence,

decreasing the total pressure of the system shifts the equilibrium to the right.