Exothermic Reaction Examples - Demonstrations to Try

Exothermic chemical reactions release heat to the environment.
Exothermic chemical reactions release heat to the environment. Dina Belenko Photography / Getty Images

 An exothermic reaction is a chemical reaction that releases heat and has a negative enthalpy (-ΔH) and positive entropy (+ΔS).. These reactions are energetically favorable and often occur spontaneously, but sometimes you need a little extra energy to get them started.

Exothermic reactions make interesting and exciting chemistry demonstrations because the release of energy often includes sparks, flame, smoke, or sounds, in addition to heat. The reactions range from safe and gentle to dramatic and explosive.

Steel Wool and Vinegar Exothermic Reaction

closeup of steel wool
The rusting of steel is an example of an exothermic chemical reaction.

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The rusting of iron or steel is an oxidation reaction -- really just a slower form of combustion. While waiting around for rust to form wouldn't make for an interesting chemistry demonstration, there are ways to speed up the process. For example. you can react steel wool with vinegar in a safe exothermic reaction that evolves heat.

Barking Dog Exothermic Reaction

A barking dog
It's called the Barking Dog because that is what the chemical reaction sounds like.

 Thomas Northcut / Getty Images

The "barking dog" reaction is a favorite exothermic chemistry demonstration because it emits a loud 'woof' or 'bark', similar to that of a dog. You need a long glass tube, nitrous oxide or nitric oxide, and carbon disulfide for this reaction.

If you don't have these chemicals, there is an alternative reaction you can do using a bottle and rubbing alcohol. It's not quite as loud or energetic, but it does produce a nice flame and an audible 'woofing' sound.

Safe Laundry Detergent Exothermic Reaction

a load of laundry and detergent
Dissolving laundry detergent in water is an exothermic reaction.

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Probably the simplest and easiest exothermic reaction is one you can try right at home. Simply dissolve powdered laundry detergent in your hand with a small amount of water. Feel the heat?

About the Laundry Detergent Exothermic Reaction

Elephant Toothpaste Exothermic Reaction

A child watching in glee as foam erupts from a flask
Use a lower concentration of peroxide for the elephant toothpaste reaction if kids will be close to the demonstration.

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No list of exothermic reactions would be complete without the popular elephant toothpaste reaction. The heat of this chemical reaction is accompanied by a fountain of foam.

The classic form of the demonstration uses a hydrogen peroxide solution, potassium iodide, and detergent. There is also a kid-friendly version of the reaction that uses yeast and household peroxide and is safe enough for young hands to touch.

Sulfuric Acid and Sugar Exothermic Reaction

sugar cubes
Dehydrating sugar produces a memorable exothermic reaction.

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Reacting sulfuric acid with ordinary table sugar (sucrose) results in an energetic exothermic reaction. Dehydrating the sugar pushes out a steaming column of carbon black, plus it makes the entire room smell like burnt marshmallows.

How to do the Sulfuric Acid and Sugar Reaction

Thermite Exothermic Reaction

Thermite reaction in a steel pan
The thermite reaction produces a lot of light in addition to heat. It's best to avoid looking directly at the flames.

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The thermite reaction is much like rusting steel wool with vinegar, except the oxidation of metal occurs much more vigorously. Try the thermite reaction is you want burning metal and a lot of heat.

If you believe "go big or go home," then try performing the thermite reaction inside a block of dry ice. This amplifies the process and may even produce an explosion.

Sodium or Other Alkali Metal in Water

sodium reacting in a container of water
Like all alkali metals, potassium reacts vigorously in water in an exothermic reaction.

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If burning metals is your cup of tea, you can't go wrong with simply dropping any alkali metal in water (unless you add too much). Lithium, sodium, potassium, rubidium, and cesium all react in water. As you move down the group in the periodic table, the energy of the reaction increases.

Lithium and sodium are fairly safe to work with. Use caution if you try the project with potassium. It's probably best to leave the exothermic reaction of rubidium or cesium in water to people who want to get famous on YouTube. If that's you, send us a link and we'll show off your risky behavior.

try the Sodium in Water Reaction (Safely)

Starting Fires Without Matches

A flame
Exothermic reactions often burst into flame without the need for a match or other ignition source.

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Some exothermic chemical reactions spontaneously burst into flame without needing the help of a lit match. There are several ways to make a chemical fire -- all terrific demonstrations of exothermic processes.

How to make Chemical Fire Without Matches

Making Hot Ice Is an Exothermic Reaction

Sodium acetate is also known as hot ice.
Sodium acetate resembles water ice, but crystallization from a supercooled solution makes these crystals hot instead of cold.

 Epop, public domain

Hot ice is what you get when you solidify sodium acetate from a supercooled solution. The resulting crystals resemble water ice, except they are hot instead of cold. It's a fun example of an exothermic reaction. It's also one of the common reactions used to make chemical hand warmers.

While you can buy sodium acetate, it's also extremely easy to make this chemical yourself by mixing baking soda and vinegar and boiling off the excess liquid.

How to make Hot Ice

More Exothermic Reactions To Try

artists rendition of exothermic reactions
If you think about it, most chemical reactions absorb heat (endothermic) or release it (exothermic), so there are thousands of exothermic reactions you can try.

Roz Woodward, Getty Images 

Many chemical reactions release heat, so these popular exothermic reactions are not your only options. Here are some other cool demonstrations to try: