What type of reaction does a catalyst primarily affect?

A catalyst primarily affects chemical reactions by increasing their rate without being consumed in the process. It accomplishes this by lowering the activation energy required for the reaction to proceed. This means that more molecules can successfully collide with enough energy to undergo the transformation into products, leading to an enhanced rate of reaction.

In the context of combustion, redox, and physical reactions, while catalysts can be involved in some specific types of these reactions, their primary role is in chemical reactions overall. They are used in various chemical processes, from industrial manufacturing to biochemical reactions in living organisms, demonstrating their broad significance across different types of chemical transformations.