IGCSE Chemistry 0620 - Chemical Reactions

Rate of Reaction - Catalysts

Objective

State that a catalyst increases the rate of a reaction and is unchanged at the end of a reaction.

What is a Catalyst?

A catalyst is a substance that speeds up the rate of a chemical reaction without being consumed in the reaction itself. It provides an alternative reaction pathway with a lower activation energy.

How Catalysts Work

Catalysts work by providing a surface or a different mechanism for the reactants to interact. This lowers the activation energy, meaning less energy is required for the reaction to occur. The catalyst participates in the reaction mechanism but is regenerated at the end, so it remains unchanged in quantity.

Types of Catalysts

There are two main types of catalysts:

• Homogeneous Catalysts: These catalysts are in the same phase as the reactants (e.g., a gas catalyst in a gaseous reaction).
• Heterogeneous Catalysts: These catalysts are in a different phase from the reactants (e.g., a solid catalyst in a liquid reaction).

Example: Enzyme Catalysis

Enzymes are biological catalysts. They are proteins that speed up biochemical reactions in living organisms. Enzymes have a specific active site that binds to the reactant molecules (substrates), facilitating the reaction.

Catalyst Remains Unchanged

A key characteristic of a catalyst is that it is not permanently used up in the reaction. The catalyst participates in the reaction mechanism, but it is regenerated at the end of the process. This means that a small amount of catalyst can speed up a large amount of reactant.

Table Summary

Feature	Description
Definition	A substance that speeds up a chemical reaction without being consumed.
Effect on Reaction Rate	Increases the rate of reaction.
Consumption	Unchanged at the end of the reaction.
Types	Homogeneous (same phase as reactants) and Heterogeneous (different phase from reactants).

Figure: Suggested diagram: A diagram showing a reaction with a catalyst, illustrating the catalyst on one side of the equation and being regenerated on the other. Label the reactants, products, catalyst, and activation energy.