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In the last lesson, we discussed chemical equilibrium as a dynamic situation where a reversible reaction is continuously taking place; reactants are transformed into products, and products are transformed into reactants.

The balance of reactant and product amounts in chemical equilibriums can be mathematically calculated using reaction equilibrium equations and equilibrium constants.

Equilibrium Equation

In a reaction with reactants (and B) and products (and D), a general equilibrium equation is written:

aA bB ↔ cC dD

with the lower case letters indicating reaction coefficients (number of molecules), and the double arrow indicating the dynamic back–and–forth nature of the reaction. The equilibrium equation is used to determine the reaction's equilibrium constant.

An equilibrium constant (Keq ) is the ratio of the product of oroduct amounts over the product of reactant amounts.