Question

Do exothermic reactions obey the law of conservation of energy?

Answer 1

Yes. All reactions obey the law of conservation of energy.

The law states that energy cannot be gained or lost, but it can be transformed into another form. Exothermic reactions releases energy as heat.

Answer 2

Exothermic reaction, has less chemical energy all combustion reactions are exothermic.
 All chemical reactions obey the law of conservation of energy. The law of conservation of energy states that energy cannot be created or destroyed.