The reaction quotient 'Q' measures the relative amounts of products and reactants present during a reaction at any point in time. It is the same expression as the equilibrium constant, but doesn't imply that the system is at equilibrium.
The ratio of concentrations of products to reactants at equilibrium.
Le Chatelier's Principle: A principle stating that if a change is made to a system at equilibrium, the system will adjust itself to partially counteract that change.