======Endothermic and Exothermic Dissolving======


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**Alternative titles:** Hot and Cold Packs, Energy Changes When Substances Dissolve
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====Summary====                   
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====Procedure====  
 - Put on safety goggles and gloves.  
  - **Experiment 1 (Endothermic):**  
    - Place a small amount of solid ammonium chloride and solid barium hydroxide in a beaker.  
    - Stir the mixture with a glass rod.  
    - Observe how the temperature drops sharply, and note that the beaker feels very cold (sometimes cold enough to freeze water underneath).  
  - **Experiment 2 (Exothermic):**  
    - Place a small piece of calcium carbonate (e.g., marble chip) into a beaker.  
    - Add dilute sulfuric acid.  
    - Observe the reaction: fizzing/bubbling due to carbon dioxide release, and the beaker becoming warm as heat is released.  
  - Compare the temperature changes in both experiments.



====Links==== 
demonstration of exothermic and endothermic reactions - Mireille Tannous: 
{{youtube>NHOHKH3808c?}}\\

Hot Pack vs Cold Pack - Exothermic vs Endothermic Chemical Reactions - Ed Reeves: 
{{youtube>u8ZmX9tJ3v8?}}\\

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

====Variations====
  * 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.



====Safety Precautions====
  * 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.




====Questions to Consider====
  * 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.)