AQA GCSE FOUNDATION Chemistry: Reversible Reactions

AQA GCSE Foundation Chemistry: Reversible Reactions

What are Reversible Reactions?

Imagine you're making a sandwich. You put bread, cheese, and ham together. This is like a forward reaction. You've created a sandwich! But, what if you decide you don't like the sandwich anymore? You can take it apart, separating the bread, cheese, and ham. This is like a reverse reaction.

In chemistry, many reactions don't just go in one direction. They can go forwards and backwards. These are called reversible reactions.

Symbols and Equilibrium

We use special symbols to show reversible reactions:

• Forward Reaction: A + B ? C + D
• Reverse Reaction: C + D ? A + B
• Reversible Reaction: A + B ? C + D

The double arrow (?) tells us the reaction can go both ways.

Equilibrium is a state where the forward and reverse reactions are happening at the same rate. This means the amounts of reactants and products remain constant. It's like the sandwich is constantly being made and unmade at the same time!

Factors Affecting Equilibrium

Several factors can affect where the equilibrium lies (whether there's more reactants or products):

• Temperature: Increasing the temperature favors the endothermic reaction (the one that absorbs heat).
• Pressure: Increasing pressure favors the reaction that produces fewer gas molecules.
• Concentration: Increasing the concentration of reactants favors the forward reaction. Decreasing the concentration of products favors the reverse reaction.

Example:

The reaction between hydrogen and iodine to form hydrogen iodide is reversible:

H?(g) + I?(g) ? 2HI(g)

• Forward Reaction: Hydrogen and iodine react to form hydrogen iodide.
• Reverse Reaction: Hydrogen iodide decomposes to form hydrogen and iodine.

At equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction.

Practical Examples

• Hydration of Ethene: Ethene (C?H?) reacts with water to form ethanol (C?H?OH). The reaction is reversible.
• Haber Process: Nitrogen and hydrogen react to form ammonia. The reaction is reversible and used to make fertilizers.

Summary

• Reversible reactions can proceed in both directions.
• Equilibrium is a state where the forward and reverse reaction rates are equal.
• Factors like temperature, pressure, and concentration can affect the position of equilibrium.
• Reversible reactions have many important applications in chemistry and industry.