Question

For the equilibrium reaction ${H_2}{O_{(l)}} \rightleftharpoons {H_2}{O_{(g)}}$ what happens when pressure is applied
a) More water evaporates
b) Boiling point of water is increased
c) No effect on boiling point
d) None of the above

Answer 1

When in a chemical reaction the state in which both the reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the system is termed as chemical equilibrium.

Complete answer:
When a chemical reaction achieves a state of equilibrium it is also said that system is in a dynamic state.In a chemical equilibrium it may look like the system is not undergoing any change however this is not true.The rate of forward reaction equals the rate of backward reaction.We can also say that the rate of formation of products is equal to the rate of formation of reactants.
But maintaining a system in chemical equilibrium is very difficult.The slightest disturbance by external factors like change in temperature,change in pressure or change in volume will shift the reaction either towards the right or left.
In the above question we can observe that we are experimenting on a system which has achieved equilibrium in the liquid and vapour phase of water.When we apply pressure on this system the equilibrium gets shifted to the left as $\vartriangle n$ is positive.This result in increase in boiling point.

Hence the correct option is (b).

Note:
The shifting of equilibrium to the left favoured the liquid phase of water.On the other hand if the pressure on the system was reduced it would have caused the equilibrium to shift towards the right and would have brought a decrease in boiling point.