Designing Heating & Cooling Reactions
Aligned to MS-PS1-6 — Next Generation Science Standards.
What this lesson teaches
Some chemical reactions release thermal energy (exothermic) and warm their surroundings, while others absorb thermal energy (endothermic) and cool them. Engineers use both to design hand warmers and cold packs.
Worked examples
Example 1
A cold pack works because dissolving ammonium nitrate in water is endothermic — it absorbs heat from your skin, so the pack feels cold and soothes a swollen ankle.
Example 2
A hand warmer is the opposite: iron powder oxidizing is exothermic, so it releases heat into your glove.
Example 3
Whether a reaction releases or absorbs heat is not something you can choose. It depends on the bonds, and a designer picks the reaction to fit the job.
Practice questions
- Observe the temperature change when two substances are mixed and classify the reaction as exothermic or endothermic.
- Design a device that keeps a drink warm using an exothermic reaction, and sketch and label it.
- Explain how you would test and modify your device to release its heat more slowly.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Diseñar Reacciones que Calientan y Enfrían
Algunas reacciones químicas liberan energía térmica (exotérmicas) y calientan su entorno, mientras que otras absorben energía térmica (endotérmicas) y lo enfrían. Los ingenieros usan ambas para diseñar calentadores de manos y compresas frías.
Ejemplo 1: Una compresa fría funciona porque disolver nitrato de amonio en agua es endotérmico — absorbe calor de tu piel, así que la compresa se siente fría y alivia un tobillo hinchado.
Ejemplo 2: Un calentador de manos es lo contrario: el polvo de hierro oxidándose es exotérmico, así que libera calor en tu guante.
Ejemplo 3: Que una reacción libere o absorba calor no es algo que elijas. Depende de los enlaces, y quien diseña escoge la reacción que sirva para el trabajo.
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