Chemistry » Chemical Equilibrium » Le Chatelier's Principle

Factors Affecting the Equilibrium Constant

Factors that influence the value of $$\text{K}_{\text{c}}$$

Concentration, pressure, and temperature all affect the equilibrium position of a reaction, and a catalyst affects reaction rates. However, only $$\color{red}{\textbf{temperature}}$$ affects the value of $$\text{K}_{\text{c}}$$.

• Changing $$\color{blue}{\text{concentration}}$$:

• Changing the concentration of a reactant or product results in one of the reactions (forward or reverse) being favoured.

• This change in reaction rate minimises the effect of the change and restores the concentration ratio between reactants and products. There will just be more reactants and products.

• $$\color{blue}{\text{K}_{\text{c}}}$$ $$\color{blue}{\text{will remain the same}}$$.

• Changing $$\color{orange}{\text{pressure}}$$:

• Changing the pressure of the system will change the ratio between the reactant and product concentrations.

• The equilibrium then shifts to minimise the effect of the change and restores the ratio between reactant and product concentrations.

• $$\color{orange}{\text{K}_{\text{c}}} \color{orange}{\text{ will remain the same}}$$.

• Adding a $$\color{purple}{\text{catalyst}}$$ to the system:

• Both the forward and reverse reactions rates are increased.

• Therefore the ratio between reactant and product concentrations will remain the same.

• $$\color{purple}{\text{K}_{\text{c}}}\color{purple}{\text{ will remain the same}}$$.

• Changing $$\color{red}{\text{temperature}}$$:

• Changing the temperature will favour either the endothermic or exothermic reaction.

• The ratio between the concentration of the reactants and products will change.

• $$\color{red}{\text{K}_{\text{c}}}$$ $$\color{red}{\text{will change}}$$.

Important:

So make sure that when comparing $$\text{K}_{\text{c}}$$ values for different reactions, the different reactions took place at the same temperature.