Demonstrating an Endothermic Reaction

Title: Endothermic (heat absorbing) reaction from 2 common household substances


In this experiment, we will do a simple experiment with citric acid and baking soda that absorbs heat and makes the surface cooler.

Difficulty: Easy


  1. Baking Soda : half tablespoon

  2. Citric Acid crystal : half Tablespoon

  3. 1 cup of water

  4. Erlenmeyer flask

  5. Thermometer

  6. A small balloon

  7. A crucible or a mixing bowl


1. In a mixing bowl, add baking soda and Citric acid crystal and mix them

2. Add this mixture inside the balloon you are using for the experiment.

3. Add 1 cup of water to the flask

4. Cover the flask with the balloon such that the chemicals inside the balloon do not fall inside

5. Measure the temperature of the test tube using the thermometer

6. Lift the balloon and let the chemicals fall into the water in the flask

6. Immediately, the reaction starts and bubbles of Carbon dioxide will start forming

8. The balloon will start expanding, with the carbon dioxide produced from the reaction.

9. Measure the temperature. The temperature would be lower than the initial temperature

Here is a video of this experiment

How It Works:

In the presence of water, Citric Acid reacts with Sodium Bicarbonate (Baking Soda) creating Sodium Citrate, water and carbon dioxide

C6H8O7 + 3NaHCO3 → Na3C6H5O7 + 3H2O + 3CO2

There will be no reaction if water is not present. Any acid including Citric acid produces Hydrogen ions in water. These hydrogen ions react with Sodium bicarbonate to complete the reaction.

Because this is an endothermic reaction, the flask where the experiment is being conducted will turn colder during the experiment.

In an endothermic reaction, the chemical energy of the final products in the reaction is greater than the total chemical energy of the reactants. During the reaction, heat from the surroundings will be absorbed by the reactants to complete the reaction.

One very common example for an endothermic reaction is the common ice pack that we use on sprained knees. The ice pack is usually comprised of a pouch of Ammonium nitrate kept inside a pouch of water. When we press the ice pack, the pouch inside is crushed, making the Ammonium Nitrate mix with water forming Ammonium and Nitrate ions as shown below

To complete the reaction, it absorbs heat from the surroundings resulting in the ice pack becoming cold to touch

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