Endothermic or Exothermic Reaction?

This simple activity materialized when I considered the temperature change obvious to a student as he completed a simple chemical reaction in his  Baking Soda and Vinegars project last year. You can access that activity at: Baking Soda and Vinegar Reactions. Students create a reaction with baking soda and vinegar, and decide whether the reaction was endothermic or exothermic based on the results they observe. This activity should be completed after instruction on chemical reactions, the law of conservation of energy, and endothermic and exothermic reactions.


  • chemical reaction - the process by which a chemical change is caused - bonds are broken and formed to rearrange atoms.
  • law of conservation of energy - energy cannot be created or destroyed but only changed from one form to another 
  • endothermic reaction - a chemical change in which energy is absorbed - usually as heat (usually causes a decrease in temperature)
  • exothermic reaction - a chemical change in which energy is released usually as heat
  • thermal energy - energy that comes from the temperature of matter


  • Prepare materials for each lab group as per materials section
  • Place Baking soda into a medium sized bowl for use by students in all groups
  • Pour vinegar into an easily accessible measuring cup or bowl


  • 1 Talking LabQuest for each lab group. More information is available here: Sci-Voice Talking LabQuest 2 Now Available. If not available, use the thermometer that is available in class. There are several thermometers highlighted on this site which are much more affordable. For example, there is a talking thermometer available from APH (Talking Thermometer from APH) and a digital talking thermometer from Thermoworks (Thermoworks Digital Talking Thermometer Probe). 
  • Vernier temperature probe for each group (also available from Independence Science)
  • 1 small bowl for each group
  • vinegar 
  • baking soda
  • measuring spoons with metric units


  1. Briefly review  exothermic and endothermic reactions.  Remind students of the differences between exothermic reactions and endothermic reactions.
    • Ask - What would we expect to happen during an exothermic reaction? --  Heat would be released - Temperature increases.  
    • What would be expected to happen during an endothermic reaction? Heat absorbed - Temperature decreases. 
  2. Tell students that we will be combining 2 substances - vinegar and baking soda  and determining what type of reaction occurs based on temperature before and after the reaction.
  3. Some of the students will likely be familiar with this reaction. 
  4. Measure 20 mL vinegar into the small bowl.
  5. Using the Vernier Talking LabQuest and the temperature probe  (or other thermometer) have students measure and record the temperature of the vinegar.
  6. Measure 10 mL of baking soda. 
  7. Each group will add the 10 mL of baking soda simultaneously.
  8. Observe and discuss the evidence of a chemical reaction - fizzing - production of a gas - Discuss
  9. Tell students that there is another evidence of a chemical reaction which has occurred.  Have each group measure the temperature after the reaction is complete and record the measurement.
  10. Discuss the results.  Students will notice that there has been a decrease in temperature.
    • Ask:  Was this an endothermic reaction or an exothermic reaction?
Students may answer the following questions in written form if time allows:
  1. What type of reaction occurred - exothermic or endothermic?
  2. What is the evidence that you observed?


If the Talking LabQuest is not available, have students gauge the temperature before and after with sighted assistance using a nonadapted thermometer.

NGSS Standards: 

Middle School

PS1.B: Chemical Reactions
Substances react chemically in characteristic ways. In a chemical process, the atoms that make up the original substances are regrouped into different molecules, and these new substances have different properties from those of the reactants. (MS-PS1-2),(MS-PS1-5) (Note: This Disciplinary Core Idea is also addressed by MS-PS1-3 Some chemical reactions release energy, others store energy. (MS-PS1-6)

High School

PS1.B: Chemical Reactions
Chemical processes, their rates, and whether or not energy is stored or released can be understood in terms of the collisions of molecules and the rearrangements of atoms into new molecules, with consequent changes in the sum of all bond energies in the set of molecules that are matched by changes in kinetic energy.(HSPS1- 4),(HS-PS1-5)
PS3.B: Conservation of Energy and Energy Transfer
Conservation of energy means that the total change of energy in any system is always equal to the total energy transferred into or out of the system. (HS-PS3-1)
Energy cannot be created or destroyed, but it can be transported from one place to another and transferred between systems. (HS-PS3-1), (HS-PS3-4)
Collage of endothermic reaction

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