Equilibrium Position (Chemistry)
Contents
Key Stage 4 Higher
Meaning
Equilibrium position is the the ratio of reactants to products when a reversible reaction is in a state of dynamic equilibrium.
About the Equilibrium Position
- The equilibrium position can be affected by the temperature and by the pressure.
- The availability of raw materials can affect the choice of equilibrium position. Where those raw materials are rare or expensive it is better to have an equilibrium position which strongly favours the forward reaction.
Temperature and Equilibrium Position
- An increase in temperature will increase the rate of an endothermic reaction it requires energy from the environment to take place.
- This means for an endothermic forward reaction a higher temperature will result in more product being formed. However, for an exothermic forward reaction less product will be formed as the back reaction will be endothermic and would increase its rate with higher temperature.
- High temperatures are more expensive because they require energy to maintain a high temperature. This means it may be more cost effective not to go for the best equilibrium position for the reaction.
Pressure and Equilibrium Position
- For reactions involving a gas as either one of the reactants or products changing the pressure will affect the position of dynamic equilibrium.
- The number of moles of gas in the reactants and products will determine which direction of reaction is favoured by higher pressure.
- If the forward reaction produces more moles of gas than the back reaction then high pressure will reduce the amount of products formed.
- If the forward reaction produces less moles of gas than the back reaction then high pressure will increase the amount of products formed.
Examples
Hydrogen + Nitrogen ⇌ Ammonia
\( 3H_2(g) + N_2(g) ⇌ 2NH_3(g) \)
- In this reversible reaction there are more moles of gas in the reactants than the products so higher pressure will favour the forward reaction and the equilibrium position will have a greater concentration of products than reactants.
Ammonium Chloride ⇌ Ammonia + Hydrochloric Acid
\( NH_4Cl(s) ⇌ NH_3(g) + HCl(g) \)
- In this reversible reaction there are more moles of gas in the products than the reactant so higher pressure will favour the back reaction and the equilibrium position will have a greater concentration of reactant than reactants.