======Freeze a Beaker to a Board======


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**Materials: **{{$demo.materials_description}}\\
**Difficulty: **{{$demo.difficulty_description}}\\
**Safety: **{{$demo.safety_description}}\\
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**Alternative titles:** Ammonium Nitrate and Barium Hydroxide Cooling, Endothermic Reaction
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====Summary====                   
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====Procedure====  
  - Place a 100 mL beaker on top of a wooden block.  Put some water between the beaker and block.
  - Add 17 g of ammonium nitrate and 32 g of barium hydroxide into the beaker at the same time.  
  - Stir the mixture with a glass rod until the reaction begins.  
  - Observe the beaker cooling rapidly; water freezes between the beaker and block, causing them to stick together.



====Links==== 
Freezing Beaker to Wood Demonstration AP Chem - BAMChem: 
{{youtube>peTn2Y5zVyM?}}\\

Christmas Science | It’s feeling cold | The endothermic reaction - STEM Learning: 
{{youtube>K02Rp4KlseU?}}\\

📄 Endothermic Reaction - Freeze a Beaker to a Board - LibreTexts: [[https://chem.libretexts.org/Courses/University_of_California_Davis/UCDemos/Endothermic_ReactionFreeze_a_Beaker_to_a_Board]]\\

====Variations====
  * Compare this demonstration with an exothermic reaction, such as dissolving calcium chloride, to highlight differences.  
  * Place a thermometer into the mixture to record the extreme temperature drop.  
  * Use other endothermic salt dissolution reactions (e.g., potassium chloride) to compare cooling effects.



====Safety Precautions====
  * Perform the demonstration in a well-ventilated space or fume hood, as ammonia gas is released.  
  * Wear lab coat, safety goggles, and nitrile gloves at all times.  
  * Handle soluble barium compounds with care—they are toxic if ingested or absorbed.  
  * Dispose of the spent solution properly by sealing and returning it for hazardous waste disposal.




====Questions to Consider====
  * Why does this reaction cause the beaker to freeze to the block? (The reaction absorbs heat from the surroundings, cooling the beaker so much that water vapor condenses and freezes.)  
  * How does this illustrate the difference between endothermic and exothermic reactions? (Endothermic reactions absorb heat, while exothermic reactions release heat.)  
  * Why does spraying water on the block help the reaction? (It ensures that enough moisture is available to freeze and create adhesion.)  
  * What everyday products rely on endothermic reactions? (Examples: cold packs used for injuries.)