Exothermic Reactions
Exothermic Reactions is when a chemical change gives off heat, like the warm foam that bursts from an elephant toothpaste experiment.
When you bake cookies, the oven gives off heat as the dough changes into crispy treats. Something similar happens in an exothermic reaction. A chemical change rearranges atoms into new substances, and that rearrangement releases stored energy as heat. The heat you feel near the reaction is energy escaping, just like the warmth that flows out when you open a hot oven door.
Explaining exothermic reactions by grade level
When you mix hydrogen peroxide with yeast and soap, the bottle gets warm and foam pushes out fast. That warmth comes from inside the mixture. The ingredients change into something new, and that change releases heat you can feel with your hands. The foam rises because the reaction also makes a gas.