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.

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