Equilibrium
 Chemical equilibrium is an idea which describes the behavior of chemical reactions over time. In reactions that have finished reacting and have attained equlibrium, the concentrations of the reactant and product chemicals do not change. For some reactions, the equilibrium constant is very large, in which case nearly all of the reactant chemical is turned into products, such as when paper is burned. For other reactions, it is very small, which results in very little product being formed. If the equilibrium constant is close to 1, a mixture of both products and reactants is expected at equilibrium. When chemists talk about equilibrium constants, they call reactions with large K values favorable and reactions with small K values unfavorable.