Equilibrium is when both reactants and products are present in concentrations which have no further tendency to change with time. Usually, this state results when the forward reaction proceeds at the same rate as the reverse reaction. Depending on conditions, a reaction can proceed in the forward or in the reverse direction. In a closed system, reversible reactions undergo dynamic equilibrium. The reaction continues but the concentrations of the reactants and products does not change. If there is a change in the conditions of the equilibrium, the position of equilibrium can change, favoring the products or the reactants. Another way of saying this is that in changing the conditions of the system, it is possible to change the rate of the forward or reverse reaction. Le Chatelier’s Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counter the changes. Another way of saying this is that the system is always seeking equilibrium. In the simplest case, assume the reactants are A and the products are B. By decreasing the concentration of A, the reverse reaction would occur, producing more of the starting materials. Likewise, if the concentration of B increased, the reverse reaction would also occur, producing more of the starting materials. Increasing the temperature of a system in dynamic equilibrium causes the system to favor an endothermic reaction, absorbing the additional heat. Alternatively, decreasing the temperature of a reaction in dynamic equilibrium favors an exothermic reaction, the system produces more heat.