What role does a catalyst play in a chemical reaction?

A catalyst plays a significant role in increasing the rate of a chemical reaction by lowering the activation energy, which is the energy barrier that reactants must overcome for a reaction to occur. By providing an alternative pathway with a lower energy requirement, a catalyst allows the reaction to proceed more easily and quickly.

Importantly, a catalyst is not consumed in the reaction, meaning it can participate repeatedly in multiple reaction processes without undergoing any permanent change. This characteristic enables catalysts to be highly effective even in small amounts and is essential for their role in many industrial and biological processes.

The other options present misunderstandings of what a catalyst does. For instance, catalysts do not affect the size of products formed, the equilibrium constant, or exclusively influence yield. While catalysts can affect reaction rates and potentially lead to changes in yield by enabling reactions to occur more efficiently, they do not directly determine the yield since that is more influenced by thermodynamic factors and reaction conditions. Thus, the correct understanding of a catalyst's function centers around its ability to lower activation energy without being consumed in the process.