Equilibrium Constant

In chemistry, the equilibrium constant, denoted as ${K}_c$, quantifies the ratio of the concentrations of products to reactants at equilibrium for a reversible reaction. It is a crucial concept in understanding chemical equilibria.

Definition

For a general reaction: $aA + bB \rightleftharpoons cC + dD$ The equilibrium constant is expressed as: ${K}_c = \frac{[C]^c [D]^d}{[A]^a [B]^b}$ where:

• $[C]$, $[D]$, $[A]$, and $[B]$ are the equilibrium concentrations of the species.
• $a$, $b$, $c$, and $d$ are the coefficients from the balanced chemical equation.

Example

Consider the reaction: $2H_{2}(g) + O_{2}(g) \rightleftharpoons 2H_{2}O(g)$ The equilibrium constant expression is: $K_c = \frac{[H_{2}O]^{2}}{[H_{2}]^{2} [O_{2}]}$

Steps to Calculate ${K}_c$:

1. Write the balanced equation.
2. Identify the concentrations at equilibrium.
3. Substitute the values into the equilibrium expression.
4. Calculate $K_c$.

Key Questions

• What factors can affect the value of the equilibrium constant?
• How do you interpret the value of $K_c$?
• What is the difference between $K_c$ and $K_p$?

Summary

The equilibrium constant is a fundamental concept in chemical equilibrium that allows chemists to predict the direction of a reaction and the concentrations of reactants and products at equilibrium.