Many a match to ignite the flame? The

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.

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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.

Exothermic reactions are also very common in the chemistry lab. Many experiments involve acids. An acid’s strength is determined by the amount it dissociates or breaks down when exposed to water. When an acid enters water, it releases hydrogen ions.

As a result of this release, heat is given off. This release can often be very violent and cause the solution to boil so quickly that it can shatter the glass container holding the mixture.Every time you start and drive your car, you are participating in an exothermic reaction. The reaction that takes place in the engine of a car is known as a combustion reaction. It involves the burning of gasoline or diesel fuel to produce and release energy that is converted to mechanical energy that moves the vehicle. This is why your car must have a cooling system and water circulation to lower the temperature that is produced by the exothermic reactions taking place.

Lesson Summary

Chemical reactions occur naturally and in the lab. Any reaction that gives off energy is considered to be an exothermic reaction. The energy given off is usually as a result of bonds being broken. The energy can be in the form of heat, light, sound, or electricity.

Important Definitions

An exothermic reaction
  • Chemical Reactions: natural & man-made reactions between elements or compounds
  • Exothermic Reactions: chemical reactions that emit energy
Exothermic Reaction Examples
Wood match
Acid & water
Combustion engines

Learning Outcomes

The goal of this lesson on exothermic reactions is to enhance your capacity to:

  • Contrast exothermic and chemical reactions
  • Detail examples of lab and man-made exothermic reactions

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