 There are a number of ways in which energy can be released in an exothermic reaction. In combustion, the most obvious way is that the energy is released in the form of heat. But notice that a flame gives light too, so combustion reactions often release light as well as heat. In fact, both light and heat are forms of the same kind of energy, electromagnetic radiation. In luminescent reactions, the energy is released as visible light without heat, which is why these reactions are sometimes called cold light. Glow sticks and the flashing of fireflies and glow worms are examples of luminescent reactions. Chemical explosives release energy as mechanical energy and sound as well as heat and light. Touch powder is a very unstable compound that explodes when it's touched. It gives off heat, but the most obvious form of energy released by this reaction is sound energy, which is a kind of mechanical energy. Respiration is the chemical reaction that living things use to turn glucose and oxygen into carbon dioxide water and energy. That's a combustion reaction, but in the bodies of organisms it occurs in a slow and controlled fashion so there's no flame involved. Nevertheless, it does produce heat, which is where the heat comes from that keeps us warm-blooded animals warm. And fireworks produce all sorts of energy at once, heat, light and sound.