# Equilibrium Concentrations of Products/Reactants

Does increasing the concentration of reactants mean the equilibrium concentration of the products will be greater (than the concentration of the reactants?)

• See this post.
– ashu
Commented Feb 4, 2015 at 5:26

Adding a reactant increases the concentration of products at equilibrium, but it doesn't necessarily mean that the product concentrations will be larger than the reactant concentrations at equilibrium.

Suppose you have a reaction $\ce{A <=> B}$. Then $$K = \frac{[\ce{B}]}{[\ce{A}]}$$ where $[\ce{A}]$ and $[\ce{B}]$ are the concentrations at equilibrium and $K$ is a constant. The ratio $[\ce{B}]/[\ce{A}]$ is constant at equilibrium, so if you add some $\ce{A}$ to the system, some $\ce{A}$ must react and become $\ce{B}$ to maintain the ratio. The equilibrium concentration of the products will increase.

But that increase in product concentration won't necessarily mean that the equilibrium product concentration becomes higher than that for the reactants. If $K$ is bigger than one, the equilibrium concentration of the products will be greater than that for the reactants; if it's less than one, the equilibrium concentration of the reactants is bigger.