Question

An unknown substance undergoes a chemical change that gives off heat. What can you tell me about this substance?

Answer 1

On a molecular level there is a lot of movement which in turn is the reason why heat is generated.

Answer 2

Explanation:

A chemical reaction in which heat is absorbed by the reactant molecules is known as an endothermic reaction.

For example, $A + B + Heat \rightarrow AB$

On the other hand, a chemical reaction in which heat energy is released by the reactant molecules is known as an exothermic reaction.

For example, $A + B \rightarrow AB + Heat$

Thus, we can conclude that when an unknown substance undergoes a chemical change that gives off heat then it means earlier the substance has more heat energy but after the chemical change there occurs a decrease in its heat energy because some of the heat has been released by it.