AQA GCSE FOUNDATION Chemistry: Dynamic Equilibrium

AQA GCSE Foundation Chemistry: Dynamic Equilibrium

What is Dynamic Equilibrium?

Dynamic equilibrium is a state where the rates of the forward and reverse reactions in a reversible reaction are equal. This means that the concentrations of reactants and products remain constant over time, even though the reaction is still happening.

Reversible Reactions

A reversible reaction is a chemical reaction that can proceed in both directions. This is represented by using double arrows in the chemical equation:

A + B ? C + D

Where:

• A and B are reactants
• C and D are products

Factors Affecting Equilibrium

Several factors can shift the position of equilibrium, favouring either the forward or reverse reaction. These are:

• Temperature:

  • Endothermic Reactions: Increasing temperature favours the forward reaction (heat is absorbed).
  • Exothermic Reactions: Increasing temperature favours the reverse reaction (heat is released).

• Pressure:

  • Increase in Pressure: Favours the side with fewer gas molecules.
  • Decrease in Pressure: Favours the side with more gas molecules.

• Concentration:

  • Increasing Reactant Concentration: Favours the forward reaction.
  • Increasing Product Concentration: Favours the reverse reaction.

Le Chatelier's Principle

Le Chatelier's Principle states that if a change of condition is applied to a system in equilibrium, the system will shift in a direction that relieves the stress.

In simpler terms, if you change something (like temperature, pressure, or concentration), the reaction will try to counteract that change.

Examples:

• Increasing Temperature in an Endothermic Reaction: The equilibrium will shift to the right, favouring the forward reaction to absorb more heat.
• Increasing Pressure in a Reaction with More Gas Molecules on the Reactant Side: The equilibrium will shift to the right, favouring the forward reaction to decrease the number of gas molecules.
• Adding More Reactant: The equilibrium will shift to the right, favouring the forward reaction to consume the excess reactant.

Key Points:

• Dynamic Equilibrium: The rates of the forward and reverse reactions are equal.
• Reversible Reactions: Reactions that can proceed in both directions.
• Le Chatelier's Principle: The system will shift to relieve stress.
• Factors Affecting Equilibrium: Temperature, pressure, and concentration.

Practice Questions:

1. What is dynamic equilibrium?
2. Explain Le Chatelier's Principle.
3. How does increasing temperature affect an exothermic reaction at equilibrium?
4. Explain how a decrease in pressure can shift an equilibrium to the right.
5. What happens to the equilibrium position when more product is added to a reversible reaction?