Here's why:
* Reactions have different activation energies: Some reactions are spontaneous at room temperature, while others require energy input (like heat) to overcome their activation energy barrier and proceed.
* Reagents can be reactants or products: A reagent can be a reactant that needs heat to start a reaction, or it can be a product that's formed by a reaction requiring heat.
* Many factors influence reactivity: Temperature is just one factor that affects reaction rates. Others include concentration, pressure, catalysts, and the presence of light.
To answer your question, I need more context.
For example, tell me:
* What specific reaction are you considering?
* What are the reactants and products involved?
* Do you have any observations about the reaction conditions?
With this information, I can help you identify the reagent(s) that may need heating to react.
