Endothermic and Exothermic Dissolving

This demonstration compares two reactions: one that absorbs heat from the surroundings (endothermic) and one that releases heat (exothermic). Students can observe changes in temperature and feel whether the container becomes hot or cold.

- Put on safety goggles and gloves.

1. Experiment 1 (Endothermic):
2. Place a small amount of solid ammonium chloride and solid barium hydroxide in a beaker.
3. Stir the mixture with a glass rod.
4. Observe how the temperature drops sharply, and note that the beaker feels very cold (sometimes cold enough to freeze water underneath).
5. Experiment 2 (Exothermic):
6. Place a small piece of calcium carbonate (e.g., marble chip) into a beaker.
7. Add dilute sulfuric acid.
8. Observe the reaction: fizzing/bubbling due to carbon dioxide release, and the beaker becoming warm as heat is released.
9. Compare the temperature changes in both experiments.

demonstration of exothermic and endothermic reactions - Mireille Tannous:

Hot Pack vs Cold Pack - Exothermic vs Endothermic Chemical Reactions - Ed Reeves:

📄 Temperature Changes in Dissolving - ACS: https://www.acs.org/middleschoolchemistry/lessonplans/chapter5/lesson9.html

• Try other common exothermic reactions, such as dissolving calcium chloride in water.
• Try other endothermic reactions, such as dissolving potassium chloride or ammonium nitrate in water.
• Use a thermometer to measure exact temperature changes for quantitative comparison.

• Always wear safety goggles and gloves.
• Handle sulfuric acid carefully—use only dilute solutions.
• Barium hydroxide is corrosive and toxic; avoid skin contact and inhalation.
• Conduct the experiments in a well-ventilated area or under a fume hood.
• Dispose of chemical waste according to school or local regulations.

• Which reaction was exothermic and which was endothermic? (Calcium carbonate + sulfuric acid is exothermic; barium hydroxide + ammonium chloride is endothermic.)
• Why does the temperature decrease in an endothermic reaction? (The reaction absorbs energy from the surroundings, lowering the temperature.)
• Why does the temperature increase in an exothermic reaction? (The reaction releases energy to the surroundings as heat.)
• What observable evidence helps distinguish these two types of reactions? (Temperature change, container hot or cold, gas release, and other visual signs.)
• How do these energy changes connect to real-life examples like cold packs and hand warmers? (Cold packs use endothermic dissolving reactions; hand warmers use exothermic crystallization or oxidation reactions.)