Question

The reaction below is exothermic: PCl3 (g) + Cl2 (g) <---> PCl5 (g) Which change will increase the number of moles of of PCl5 (g) present?

A. The volume of the reaction vessel is tripled

B. The reaction vessel is cooled

C. Some of the Cl2 is removed

D. Krypton gas is added to the reaction vessel

Answer 1

A)

We are increasing volume here

In other words we are trying to decrease pressure

so, according to Le Chatelier's principle,

Reaction will try to increase the pressure

Hence it will move in a direction which have more gaseous molecules

Here reactant has more gaseous molecule

So equilibrium will move to left

Equilibrium moves to reactant side

B)

Forward reaction is exothermic in nature

we are decreasing temperature or removing heat here

so, according to Le Chatelier's principle,

equilibrium will move in direction which release heat

hence, forward reaction will be favoured

Equilibrium moves to product side

C)

we are removing a reactant

According to Le Chatelier's Principle,

Removing reactant will shift reaction towards reactant side

Equilibrium moves to reactant side

D)

Adding noble gas will increase pressure

We are increasing pressure here

so, according to Le Chatelier's principle,

Reaction will try to decrease the pressure

Hence it will move in a direction which have lesser gaseous molecules

Here product has less gaseous molecule

So equilibrium will move to right

Equilibrium moves to product side

Answer: B and D

if it is looking for only 1 answer, go for B