Explain the impact that changing pressure has on a system in a state of dynamic equilibrium. what will happen when pressure on a reaction mixture at equilibrium and with fewer moles on the reactant side is increased?

Pressure in a system increases, the volume decreases, the equilibrium will shift to favor the side of the reaction that involves fewer moles of gas.

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 The equilibrium shifts towards the side of the reaction having a fewer moles of reactants i.e towards the reactant side.

Explanation:

When a system is in equilibrium, application of an external pressure causes the system to shift to a new equilibrium state in order to offset the condition. There, increase in pressure will make the equilibrium shift towards the side of the reaction which has a fewer moles of chemical species while the decrease in pressure cause the equilibrium to shift towards the side which has more moles of chemical species.  

Further explanation:

According to the Le Chatelier’s principle, a reaction mixture at equilibrium shifts to left side or right side in order to keep the equilibrium unchanged even we change an external factor such as pressure.

There are three major ways that we can change the pressure applied on the equilibrium; by adding or removing a reactant or a product, addition of an inert gas and changing the volume of the system.  

When the pressure is increased or decreased, the equilibrium shifts towards either reactant side or product side in order to establish a new equilibrium state.  

When we increase the pressure, the equilibrium shifts towards the side where there is a fewer moles of the chemical species.  

When we decrease the pressure, the equilibrium shifts towards the side where there are more moles of the chemical species.  

This is mainly because the pressure is inversely related to the volume of a system.

The equilibrium shifts towards the side having a fewer moles of the reactants in order to increase the amount of reactants (at the same time the amount of product should be reduced in order to keep the equilibrium state).  

Learn more:

1. Dynamic equilibrium:   (answer by Tringa0)

2. Le Chatelier’s principle and pressure change:   (answer by scme1702)

Key words:

Le Chatelier’s principle, equilibrium state, pressure, reactant, product, inert gas, volume