Why is fire hot?

Anything that burns has energy stored in it. When it burns, the energy is quickly released as heat and light, which we see as fire.

For example, energy from sunlight is stored in wood. As a tree grows, it absorbs sunlight and uses that energy to change molecules of water and carbon dioxide into larger molecules that make up the tree.

We start a campfire by heating dry wood to its kindling temperature. Then, some of the large molecules break free from the wood and rise into the air as a vapor. These molecules react with oxygen in the air and break down into water and carbon dioxide again—with a release of heat and light.

So a fire is hot because it’s a fast release of energy that was stored over years.