Question

Two common ways for a chemist to increase the yield of a reactiom are described below. Explain why they increase the yield.
a. Add more of one of the reactants
b. Remove one of the products as it is being made.

Answer 1

Le Chatelier's Principle

The state of dynamic equilibrium, in which a chemical system is reacting to form and to destroy products, is a stable state. If a system is not in equilibrium, the driving force toward equilibrium is greater than the driving force away from equilibrium and the system has a net driving force toward equilibrium. Alternatively, if a system is not in equilibrium the rate of the reaction toward equilibrium is greater than the rate of the opposite reaction so there is a net movement always toward the equilibrium state. In other words, a system at equilibrium will tend to stay at equilibrium and a system not at equilibrium will tend to more toward equilibrium.

Examples of Le Chatelier's Principle:

a) Added Reactants:

The effect of adding reactants to a system at chemical equilibrium is to increase the concentration or partial pressures of the products; the equilibrium concentrations of the reactants will be less than the sum of the original concentrations and those added due to the equilibrium reaction.

The effect of adding a reactant is to decrease the concentrations of the reactants (as well as the concentration of the reactant added, though only to the extent of part of the original increase) and to increase the concentrations of all products. The equilibrium shifts to the right when a component is added on the left, or reactant, side.

b) Remove products.

Removal of product forces the position of equilibrium to the right and increases the yield. The equilibrium is dynamic, and when the equilibrium is reached the reaction stops, so if you remove the products as it is being made you force the reaction to reach the equilibrium again producing more products. This is posible because there are still molecules of the reactants left in the space so they can react again.