The Nature of Heat: Molecular Movement

Appears in
On Food and Cooking

By Harold McGee

Published 2004

  • About

One kind of energy is the energy of motion, or kinetic energy. Atoms and molecules can move from one place to another; or spin in place, or vibrate, and all of these changes in position or orientation require energy. Heat is a manifestation of a material’s kinetic energy, and temperature is a measure of that energy: the higher the temperature of a food or pan, the hotter it is, the faster its molecules are moving and colliding with each other. And simple movement is the key to transforming molecules and foods. As molecules move faster and more forcefully, their motions and collisions begin to overcome the electrical forces holding them together. This frees some atoms to find new partners and rearrange themselves in new molecules. Heat thus encourages chemical reactions and chemical change.