When ammonium nitrate and barium hydroxide are mixed, they undergo a strongly endothermic reaction that absorbs heat, lowering the temperature to around –25 °C to –30 °C. The beaker becomes so cold that water freezes, bonding the beaker to the wooden block beneath it.

1. Place a 100 mL beaker on top of a wooden block. Put some water between the beaker and block.
2. Add 17 g of ammonium nitrate and 32 g of barium hydroxide into the beaker at the same time.
3. Stir the mixture with a glass rod until the reaction begins.
4. Observe the beaker cooling rapidly; water freezes between the beaker and block, causing them to stick together.

Freezing Beaker to Wood Demonstration AP Chem - BAMChem:

Christmas Science | It’s feeling cold | The endothermic reaction - STEM Learning:

📄 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

• 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.

• 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.

• 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.)