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Endothermic and Exothermic Reactions

Contributor: Hannah Brooks. Lesson ID: 12912

Are you warming up to the idea of being a scientist, or does the idea of conducting experiments leave you cold? How would you react to knowing that when you cook, you are creating chemical reactions?



learning style
personality style
Grade Level
High School (9-12)
Lesson Type
Quick Query

Lesson Plan - Get It!


Have you ever used portable hand warmers during the winter? How do you think they produce heat?

  • How do you activate a hand warmer once you take it out of the package?

Generally, you have to shake it up. This mixes the contents, creating a chemical reaction. These chemical reactions generate heat that keeps your hands and feet warm in the cold weather! Not all chemical reactions produce heat — some actually get colder!

A reaction that generates heat is called an exothermic reaction. An exothermic reaction releases energy into the environment, often in the form of heat. Energy can also be released as electricity, light, and sound. Since energy is released, the reactants have more energy than the products, represented in the diagram below:

visual examples of exotheric energy

The difference in energy between reactants and products is equal to the amount of heat released into the environment.

  • Can you think of some examples of exothermic reactions?

Every combustion reaction represents an exothermic reaction, because heat and light are released!

examples of fire flames

  • Compare the endothermic reaction image to that of the exothermic reaction. How is it different?

In an endothermic reaction, energy is absorbed from the environment. This means that some amount of energy is needed to drive the reaction forward. Think about cooking an egg — can you cook an egg without heat? The heat is absorbed by the egg as it changes from raw to sunny-side-up.

fired egg

Products hold more energy than reactants in an endothermic reaction.

  • How do you think the temperature changes in an endothermic reaction?

The temperature goes down as the reaction becomes colder.

Endothermic and exothermic reactions occur because of differences in energy between the reactants and products in a chemical reaction. When the reactants have more energy, it is released into the environment as heat or light. The reaction generally does not require the input of energy to run. In contrast, endothermic reactions need energy for the reaction to run. These reactions absorb energy, and the products hold more energy than the reactants. The temperature decreases in an endothermic reaction.

  • How are endothermic and exothermic reactions similar? How are they different?
  • Why might the differences make them useful for different purposes in our world?

In the Got It? section, learn more about each type of reaction by watching a video!

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