Final answer:
Endorphins are the chemicals produced by the body during exercise that can make you feel happier and more peaceful.
Step-by-step explanation:
The chemical that is produced by the body when you exercise and can make you feel happier and more peaceful is endorphins. Endorphins are neurotransmitters that play a major role in the body's inhibitory response to pain. They can be triggered by vigorous aerobic exercise, such as running or cycling, and are known to contribute to the phenomenon called a 'runner's high'.