How does adding more reactant affect equilibrium?

Adding more reactant to a system at equilibrium shifts the equilibrium to the right, favouring the forward reaction.

In a chemical reaction, equilibrium is the state where the concentrations of the reactants and products do not change with time. It occurs when the rate of the forward reaction equals the rate of the reverse reaction. This concept is governed by Le Chatelier's Principle, which states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.

When you add more reactant to a system at equilibrium, you are increasing the concentration of the reactant. According to Le Chatelier's Principle, the system will respond by trying to decrease the concentration of the reactant. It does this by shifting the equilibrium to the right, favouring the forward reaction. This means that more reactant is converted into product, until a new equilibrium is established.

For example, consider the reversible reaction: A + B ⇌ C + D. If you add more of reactant A, the system will respond by shifting the equilibrium to the right, converting more A and B into C and D. This will continue until the concentrations of A and B are reduced to their original levels, at which point a new equilibrium is established.

It's important to note that while the position of the equilibrium shifts, the equilibrium constant for the reaction remains the same. This is because the equilibrium constant is determined by the relative energies of the reactants and products, which are not affected by changes in their concentrations.

In summary, adding more reactant to a system at equilibrium causes the system to shift to the right, favouring the forward reaction, in order to restore equilibrium. This is a direct application of Le Chatelier's Principle, a fundamental concept in the study of chemical equilibria.