Andrew Gellman, Lord Professor of Chemical Engineering at Carnegie Mellon University, explains how energy changes form when we use it for power or heat.

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Transcript

Where does energy go when we use it?

HOST: Have you ever wondered where the energy goes when we use it? On this week’s Energy Bite, Andy Gellman, a professor at Carnegie Mellon University, has some answers.

ANDY: You may have learned in a science class that energy is always conserved and never consumed. In other words, the total amount of energy in the universe does not change, it simply shifts from one form to another. For example, if you mix some hot water into some cold water, the energy in the hot water heats the cold water and you get warm water. The energy in the warm water equals the energy originally in the hot and the cold water.

HOST: In that case, what does it mean to ‘use’ energy?

ANDY: When we use energy we simply cause it to change from one form to another. For example, when you burn natural gas it is transformed into carbon dioxide and water. These compounds contain less energy than the natural gas. The heat released is exactly equal to the energy difference between the gas being burned and the carbon dioxide and water being produced. This heat then cooks your food or powers a car. Although the energy is not lost, it changes form, and this transformation cannot be undone.

HOST: Do you ever think about what happens when you use energy? Take our poll, see the results, and ask your energy questions at Energy Bite dot org.