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Lesson 17, Topic 1
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# The Equilibrium Constant Expression

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The position or extent of a chemical equilibrium can be expressed quantitatively using the equilibrium constant (Keq).

The equilibrium constant may be written as the following, which is based on the ratio of products to reactants of an equilibrium system at a specific temperature:

K_{\text {eq}} = \frac{ [\text{products}]}{[\text{reactants}] }

But more specifically, it is calculated using the equilibrium constant expression. For the reaction below:

a\text A + b\text B ⇌ c\text C + d\text D

the equilibrium expression is:

K_{\text{eq}} = \frac{[\text C]^c[\text D]^d}{[\text A]^a[\text B]^b}

A change in temperature is the only factor that will cause the equilibrium constant to change. Factors such as pressure, concentration and volume will simply affect the position of equilibrium.