Endothermic Chemical Reaction Science Activity

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Endothermic chemical reaction

Endothermic Chemical Reaction Science Activity Using Epsom Salt

You may have used Epsom salt and water in a garden or as a foot soak. Epsom salt and water create an interesting endothermic chemical reaction.

In this simple chemistry activity, your student will be able to feel the results of the chemical reaction, as well as to measure what happened. This is what makes it a fun demonstration and effective teaching activity.

Before we get started, let’s go over some vocabulary and concepts.

Helpful Definitions and Concepts

  • Epsom salt is magnesium sulfate, so we will use that label going forward. We will be mixing magnesium sulfate with water.
  • When the water and magnesium sulfate are mixed together it forms a solution. A solution is a mixture that has a solute and a solvent. The solute is what is being dissolved. The solvent is what the solute is dissolved into.
  • Chemical reactions and chemical changes always involve energy changes. During these reactions and changes, bonds are being made and/or being broken; these processes involve energy.
  • Since energy is involved in a chemical reaction, these reactions fall into one of two categories – an endothermic chemical reaction or an exothermic chemical reaction.
    • Both of these words have Greek origins. Exo means out, Endo means within, and thermic is from the Greek word therme, which means heat.
  • In an endothermic chemical reaction more energy is released into the surrounding area than is absorbed.
  • In an exothermic chemical reaction, more energy is released into the surrounding area than is absorbed

Let’s get started!

What You’ll Need for this Endothermic Chemical Reaction Activity

Endothermic Chemical Reaction Activity with Epsom Salt and Water


  • 1 liquid measuring cup
  • 1 dry ingredient measuring cup
  • 1 1/4 cups Room temperature water
  • 1 bowl
  • 1 paper cup
  • Epsom salt
  • Spoon
  • Thermometer


  • Set 1 ¼ cups of water out so it comes to room temperature

  • Pour ¼ cup of water into the paper cup and 1 cup of water into the bowl.

  • Measure and record the temperature of the water in the cup and in the bowl.

  • Add ½ cup of Epsom salt to the paper cup only and STIR, STIR, STIR.

  • Let sit for 30-45 seconds.

  • Take the temperature of the water in the bowl, then the temperature of the water in the cup.

  • Continue to stir a little and take the temperature of the water in the cup. What’s the temperature after 1 minute, 5 minutes, 15 minutes?


Endothermic Chemical Reaction Mixing Epsom salt and water

Epsom salt and water masuring the temp for the endothermic chemical reaction activity

What happened?

The temperature of the water in the cup went down. Have your student review the information listed at the beginning of the post.

Why do you think the temperature of the water dropped?

What do you call the magnesium sulfate & water mixture?  (a solution)

Which is the solute?  (magnesium sulfate) which is the solvent? (water)

When the magnesium sulfate and water mix, two processes are happening. First, when the water dissolves the magnesium sulfate, the water’s heat energy is used to split apart the molecules into magnesium ions and sulfate ions.

In the second process, the water molecules attach to the individual magnesium and sulfate ions, which releases energy.

In this chemical reaction, first energy is used, then energy is released. However, more energy is used when the water molecules break up the magnesium sulfate into ions than is released in the second “step” when the water molecules attach to the magnesium and sulfate ions.

This is called an endothermic chemical reaction because it takes in more energy than it produces, which leaves the surrounding area cooler than it was.

Turn This Activity Into An Experiment

To turn this into an endothermic chemical reaction experiment with a dependent and independent variable.

Here are some ideas: repeat the steps, but substitute NoSalt brand salt alternative for the Epsom salt. Or repeat the steps above substituting an ice cube for the Epsom salt.

Before starting the experiment, form your hypothesis. What do you predict will happen when the Epsom salt, No Salt, and ice are each added to the water? How will you test and measure your hypothesis? What will be the dependent variable and independent variable?

You could also test if the starting water temperature has an effect on the temperature change when water is added to the Epsom salt.

What other variable could you change, measure, and test?

Other Chemistry Resources and Activities

Endothermic chemical reaction

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