Name:______Date:______Class:______

What makes a chemical reaction endothermic or exothermic?

This activity was adapted from the lab investigation: Endothermic, Exothermic, & Chemical Change on The American Chemical Society website:

  1. Define the terms endothermic and exothermic. Be sure to include the term energy in your definition.
  2. Endothermic-
  3. Exothermic-
  4. Data Collection- In the Lab (Wear safety goggles and follow all standard safety procedures)
  5. Reaction 1- Sodium Bicarbonate and Acetic Acid
  6. Obtain a 250 mL beaker and add 20 mL of acetic acid (vinegar) to the beaker.
  7. Place the temperature probe in the beaker and allow the temperature to stabilize. Record this temperature in the data table as the initial temperature.
  8. Leave the temperature probe in the beaker and add 0.5 grams of solid sodium bicarbonate (baking soda) to the beaker. Monitor the temperature and record the final temperature in the data table once the temperature stabilizes.
  9. Wash the contents of the beaker down the drain with plenty of water.
  10. Reaction 2- Sodium Bicarbonate Solution and Calcium Chloride
  11. Add 50 mL of water to a clean 250 mL beaker and add 1.5 grams of sodium bicarbonate (baking soda) to make an aqueous sodium bicarbonate solution.
  12. Place the temperature probe in the beaker and allow the temperature to stabilize. Record this temperature in the data table as the initial temperature.
  13. Leave the temperature probe in the beaker and add 0.5 grams of calcium chloride to the beaker. Monitor the temperature and record the final temperature in the data table once the temperature stabilizes.
  14. Wash the contents of the beaker down the drain with plenty of water.

Reactants / Initial Temperature (Ti) / Final Temperature (Tf) / Temperature Change (T) / Endothermic or Exothermic?
Sodium bicarbonate (solid) + acetic acid
Sodium bicarbonate (aqueous) + calcium chloride
  1. For the reaction of sodium bicarbonate and acetic acid:
  2. Write the balanced chemical equation for the reaction: sodium bicarbonate reacts with acetic acid to form water, carbon dioxide, and sodium acetate.
  1. What evidence is there that a chemical reaction has occurred?
  1. Is this reaction endothermic or exothermic? What evidence do you have to support your claim?
  1. Recall from the video that energy is used to break bonds in the reactants and energy is released when the bonds of the products form. Based on your answer to part c is more energy required to break the bonds of the reactants in this reaction or is more energy released from the formation of the products? Explain.
  1. Develop a model to visualize the relative (non-numerical) quantity of the bond energy of the reactants and the bond energy of the products.
  1. For the reaction of sodium bicarbonate and calcium chloride:
  2. Write the balanced chemical equation for the reaction: sodium bicarbonate (aqueous) reacts with calcium chloride to form carbon dioxide gas, water, sodium chloride and calcium carbonate.
  1. What evidence is there that a chemical reaction has occurred?
  1. Is this reaction endothermic or exothermic? What evidence do you have to support your claim?
  1. Recall from the video that energy is used to break bonds in the reactants and energy is released when the bonds of the products form. Based on your answer to part c is more energy required to break the bonds of the reactants in this reaction or is more energy released from the formation of the products? Explain.
  1. Develop a model to visualize the relative (non-numerical) quantity of the bond energy of the reactants and the bond energy of the products.