A chemical catalyst (gr. katálysis = dissolution) is a substance that influences the speed of a reaction without being consumed by it. This happens as the catalyst increases or decreases the activation energy of the reaction. Energy-decreasing catalysts are referred to as positive catalysts, energy-increasing as negative catalysts. (The latter are not to be confused with inhibitors.) Thus, catalysts change the kinetics of chemical reactions without altering their thermodynamics. They equally speed up or slow down the reverse and forward reaction and do not change the equilibrium of a reaction.