5: Endothermic and exothermic

3 examples of endothermic changes

* some chemical reactions
* melting and boiling
* dissolving substances in water

Explain an example of an endothermic change.

* Cold pack
* Outer bag contains water, inner bag contains solid ammonium nitrate
* When inner bag is broken, water and ammonium nitrate mixes
* Solid dissolves in water, and mixture cools
* Injured body part transfers thermal energy to cold pack, so it feels better
* Mixture slowly returns to temp of surroundings

Explain an example of an endothermic **reaction**.

* Citric acid crystals - 20 degrees
* Add sodium hydrogen carbonate powder - there is a chemical reaction
* Reacting mixture feels cold - temp decreases to 10 degrees
* Temp decrease shows endothermic reaction

3 examples of exothermic changes

* chemical reactions ie. combustion
* freezing and condensing
* dissolving some substances in water

Explain an example of an exothermic **reaction**.

* Dilute sulfuric acid and sodium hydroxide solution - both 20 degrees
* Mixes them - chemical reaction
* Measures temperature again - 30 degrees
* Temperature increase shows exothermic reaction