Endothermic Reaction: Easy Science Activity

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Endothermic Reaction 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 measure what happened. This makes it a fun demonstration and effective teaching activity.

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

What is An Endothermic Reaction

An endothermic chemical reaction is a reaction that absorbs heat energy from its surroundings. Because heat is being absorbed, the temperature of the surroundings usually decreases.

Chemical reactions aren’t the only processes that can be endothermic. Some physical processes, including dissolving certain salts in water, can also absorb heat. In the activity below, we’ll use Epsom salt and water to observe an endothermic process and measure the temperature change.

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 magnesium sulfate dissolves in water, it forms a solution. A solution contains a solute and solvent. The solute is the substance being dissoved, in this case, magnesium sulfate. The solvent is the substance doing the dissolving, in this case water.
• Chemical reactions involve energy changes. Breaking chemical bonds requires energy, while forming new bonds releases energy.
• Chemical reactions can be classified as endothermic or exothermic based on he overall transfer of energy.
  • 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 absorbed from the surroundings than is released. This causes the surroundings, including the reaction mixture, to become cooler.
• In an exothermic chemical reaction, more energy is released to the surroundings than is absorbed. This causes the surroundings to become warmer.

Let’s get started!

What You’ll Need for this Endothermic Reaction Activity

 

 

 Questions to ask your student:

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)

What Happened?

When Epsom salt dissolves in water, the magnesium sulfate separates into magnesium ions and sulfate ions. Separating the particles requires energy. At the same time, water molecules surround and interact with the ions, which releases energy.

For Epsom salt dissolving in water, more energy is absorbed during the overall process than is released. That energy comes from the surrounding water, cuasing its temperature to drop.

Because the process absorbs more energy from the surroundings than it releases, it is endothermic.

Endothermic chemical reactions include certain reactions between baking soda and acids and reactions involved in some cold-pack demonstrations. Endothermic physical processes include melting ice, evaporation, and dissolving certain salts in water.

This chart will help students understand endothermic vs. exothermic reactions.

Turn This Activity into an Experiment

So far, you’ve demonstrated an endothermic process. Now, turn the activity into an experiment by changing one variable and measuring how that change affects the temperature.

For example, you could investigate whether the starting temperature of the water affects the amount of temperature change when Epsom salt dissolves.

Independent variable: Starting temperature of the water

Dependent variable: Change in temperature after adding the Epsom salt

Controlled variables: Amount of water, amount of Epsom salt, container, stirring time, and time before measuring the final temperature

Before you begin, make a hypothesis. What do you predict will happen? Then collect your temperature measurements and compare the results.

Here are some ideas: repeat the steps, but substitute NoSalt brand salt alternative for the Epsom salt.

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

Frequently Asked Questions About Endothermic Reactions

What is an endothermic chemical reaction?

An endothermic chemical reaction is a reaction that absorbs energy from its surroundings. When heat energy is absorbed, the surroundings usually become cooler.

Why does an endothermic reaction feel cold?

An endothermic reaction absorbs heat energy from its surroundings. If you touch the outside of the container, it may feel cold because heat is being transferred from the surroundings, including your hand, into the system.

What is the difference between an endothermic and exothermic reaction?

An endothermic reaction absorbs energy from its surroundings, while an exothermic reaction releases energy to its surroundings. Endothermic reactions often cause a decrease in the temperature of the surroundings, while exothermic reactions often cause an increase.

Is dissolving Epsom salt in water a chemical reaction?

Dissolving Epsom salt in water is better described as a physical process called dissolution rather than a chemical reaction. However, it is an endothermic process, making it a simple way for students to observe and measure how energy can be absorbed from the surroundings.

 Other Chemistry Resources and Activities

• Acids and Bases
• Testing the properties of Water
• Water Purifying Experiment
• Why Leaves Change Color In The Fall (includes 20-page free printable)
• Does your family like to garden? Incorporate a magnesium sulfate experiment along with your garden for some interesting soil science! The University of Montana Extension Service has some good chemistry information about the use of magnesium sulfate in the garden.

 

 

 

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