Question

Chemical A and Chemical B react in an exothermic reaction. What can be known about what will happen when Chemical A and Chemical B are mixed together?

The old substance will need more energy to break its chemical bonds than the new substance will release.
More energy will be released from the old substance than the new substance will release to form its chemical bonds.
The color will change as a result of the reaction.
The substance will bubble as a result of the reaction.

Answer 1

Only the idea expressed by the second statement is correct (if read the usual way): in an exothermic reaction the energy released when the new (product) bonds form is greater than the energy required to break the old (reactant) bonds, so net heat is given off.

Specifically:
- Statement 1 is false — it describes an endothermic process.
- Statement 2 (properly worded: “more energy is released when the product bonds form than was needed to break the reactant bonds”) is true for an exothermic reaction.
- Statements 3 and 4 (color change, bubbling) may occur in some reactions but are not guaranteed by an exothermic reaction alone.