Question

A scientist is studying a previously unknown chemical reaction. She concludes that it is exothermic. What must the scientist have observed?

Answer 1

The reaction released heat

Step-by-step explanation:

"Exothermic" means the reaction released some level of heat

Answer 2

The scientist observed the release of heat from the chemical reaction. An observation of this could be condensation on the glass of the beaker or steam or something else with the release of heat.