Magnitude of the Equilibrium Constant

Understanding the Equilibrium Constant

The equilibrium constant, denoted by K, is a measure of the ratio of the concentrations of products to reactants at equilibrium.
It gives a numerical value that represents the position of the equilibrium in a reversible reaction.
The equilibrium constant is dependent on temperature, and changes if the temperature of the reaction is altered.
For a general reaction: aA + bB ⇌ cC +dD, the equilibrium constant expression is given by K = [C]^c[D]^d / [A]^a[B]^b.
Square brackets denote concentrations.
Changing concentrations of reactants or products does not change the value of K but changing the temperature does.

Magnitude of the Equilibrium Constant

The magnitude of the equilibrium constant indicates the extent of a reaction at equilibrium.
If K » 1, the reaction heavily favours products at equilibrium, implying the reaction to the right (forward direction) is nearly complete.
If K « 1, the reaction heavily favours reactants at equilibrium, implying the reaction to the left (reverse direction) is favoured.
If K ≈ 1, neither reactants nor products are favoured at equilibrium, indicating the reaction is halfway complete.

Interacting with the Equilibrium Constant

The equilibrium constant can be used to predict the direction of the reaction.
When the given Q (reaction quotient) is compared to K, if Q > K, the reaction shifts left to reach equilibrium. If Q < K, the reaction shifts right to reach equilibrium.
A catalyst has no effect on the equilibrium constant as it increases the rate of the forward and reverse reactions equally.
Knowing the equilibrium constant of a reaction at a particular temperature allows calculation of concentrations of reactants or products at equilibrium.

Impact of Temperature on Equilibrium Constant

The effect of temperature on the equilibrium constant is determined by whether the reaction is exothermic or endothermic.
For an exothermic reaction, an increase in temperature decreases the value of K, shifting the equilibrium towards the reactants.
For an endothermic reaction, an increase in temperature increases the value of K, shifting the equilibrium towards the products.