Exothermic Reaction: Definition & Example

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  • 0:00 What is an Exothermic…
  • 1:28 Examples of Exothermic…
  • 2:49 Lesson Summary
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Lesson Transcript
Instructor: Derrick Arrington

Derrick has taught biology and chemistry at both the high school and college level. He has a master's degree in science education.

Many chemical reactions occur everyday and can have very different results. In this lesson, you will learn about chemical reactions that are considered to be exothermic.

What Is an Exothermic Reaction?

We usually think of chemical reactions as happening in laboratories with lots of vials and different colored solutions being poured into each other. But have you ever built a campfire using a match to ignite the flame? The fire created by the match is a chemical reaction, too!

Any process that rearranges the atoms of one or more substances to become a new substance is known as a chemical reaction. Chemical reactions are routinely completed in labs and occur as natural processes in the environment. Many chemical reactions absorb or release heat and energy as part of the process.

An exothermic reaction is any reaction that releases or gives off energy during the reaction. You can remember this by putting together 'exo-' which means to exit, with 'therm' which refers to heat. So a reaction where heat or energy leaves or is released is an exo-therm-ic reaction. (The opposite of an exothermic reaction is an endothermic one, where endo- means to absorb or let in energy.)

The energy given off can be in multiple forms, including heat, light, sound, or electricity. This energy is normally obtained as a result of bonds being broken during the reaction. In a molecule or compound, a majority of the energy is held in the bonds that link the molecules. Bonds have varying strengths. When a reaction occurs that causes these bonds to break, it gives off energy and is, therefore, exothermic.

Examples of Exothermic Reactions

Exothermic reactions are very common. Let's take our match example from the beginning. The friction that is caused when you rake the match head against a rough surface ignites the phosphorus and potassium chlorate in the head of the match and they continue to burn with the oxygen in the air. This creates a flame, which is a definite sign that an exothermic reaction is taking place as heat and energy are being given off.

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