Endothermic Reactions

Learning Outcomes

A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another.  Chemical reactions are an integral part of technology, of culture, and indeed of life itself.  An endothermic reaction is any chemical reaction that absorbs heat from its environment. The absorbed energy provides the activation energy for the reaction to occur. A hallmark of this type of reaction is that it feels cold.  This exercise will allow you to understand chemical reactions, explain what happens during an endothermic reaction and make both quantitative and qualitative scientific observations.

Materials

• 25 ml citric acid solution (can be purchased at a pharmacy over the counter or online from Amazon, granules can also be purchased and reconstituted with water)
• 15 g baking soda
• 8 oz Styrofoam cup (can use larger)
• thermometer (for part 1 and 2)
• Popsicle stirring stick

How It Works

How to Create an Endothermic Reaction

Caution:  Wear goggles and gloves.

1. Pour the citric acid solution into a coffee cup. Use a thermometer or other temperature probe to record the initial temperature. Record in the data table below.
2. Stir in the baking soda (sodium bicarbonate). Track the change in temperature as a function of time. Record the first meeting as 1 min, then continue recording the temperature in minute increments over 5 minutes.
3. With gloved hands, touch the outside of the Styrofoam cup
4. The reaction is: H3C6H5O7(aq) + 3 NaHCO3(s) → 3 CO2(g) + 3 H2O(l) + Na3C6H5O7(aq)

5. When you have completed your demonstration or experiment, simply wash the cup out in a sink. No toxic chemicals to mess with!

Additional Resources

• Chemical Reaction Lesson Plan