Impetus and Reactant

Impetus noun - Something that arouses action or activity.

Reactant and impetus are semantically related In some cases you can use "Reactant" instead a noun "Impetus".

Reactant noun - A chemical substance that is present at the start of a chemical reaction.

Impetus and reactant are semantically related in catalyst topic. You can use "Impetus" instead a noun "Reactant", if it concerns topics such as something which incites activity.