Hot and Cold Thermochemistry - Chemical Ice Packs and Hand Warmers

Dissolve a spoonful of urea in water and feel it turn cold in your hands — then heat a sodium acetate solution until it's crystal clear, cool it undisturbed, and trigger it with a single touch to watch it turn solid and warm right before your eyes. This twin experience explores enthalpy from both directions: one reaction pulls heat out of its surroundings, the other pushes heat back out into the world, and the exact same vocabulary — ΔH, calorimetry, spontaneity — explains both. Students build a working instant cold pack, grow a supersaturated "hot ice" tower, measure real temperature data with a calorimeter, and calculate enthalpy of dissolution and crystallization from scratch, comparing their results to literature values. This is the same chemistry inside every sports medicine cold pack and every reusable hand warmer, run as one connected investigation instead of two disconnected demos.

What's Included

• Urea, CO(NH₂)₂ — ~90g (3 trials)
• Sodium acetate trihydrate, NaCH₃COO·3H₂O — 80g
• Zip-lock bags × 3
  
• Nitrile gloves × 2 pairs
• Safety goggles × 2 pairs
• Printed worksheet with calorimetry calculations

You Provide

• Styrofoam or paper cups × 2, nested
• Microwave-safe container (250 mL)
• Plastic wrap
• Thermometer or infrared temperature probe
• Kitchen scale (±0.1 g accuracy ideal)
• Glass stirring rod or spoon
• Distilled water
• Shallow dish or plate

♻ Waste Disposal
Rating: Easy
Both urea and sodium acetate are non-hazardous, food-grade, and fully biodegradable. Dissolve either in water and dispose down the drain — no special disposal required. Sodium acetate can also be retained and reused indefinitely by re-dissolving.

Curriculum Connections

• NGSS HS-PS3-1 / HS-PS3-4 — Calorimetry and enthalpy measurement
• NGSS HS-PS3-2 / MS-PS3-4 — Energy models for absorbed and released heat
• AP Chemistry Units 3 & 6 — Hydrogen bonding, ionic lattice forces, thermodynamics
• IB Chemistry Topics 4, 5 & 15 — IMF, energetics, Gibbs free energy spontaneity
• Common Core HSN-Q.A.1 / HSA-CED.A.4 — Unit conversion, percent error analysis