Chemistry - 7 Energy Changes - 7.1 Exothermic and Endothermic Reactions & 7.2 Using Energy Transfers From Reactions

Exothermic reaction

a reaction that releases energy in the form of heat

Endothermic reaction

a reaction in which energy is absorbed

Neutralisation: endo- or exo-?

exothermic

Combustion: endo- or exo-?

exothermic

Examples of exothermic reactions [3]:

• neutralisation

• combustion

• respiration

Thermal decomposition: endo- or exo-?

endothermic

calcium carbonate thermal decomposition

calcium carbonate --> calcium oxide + carbon dioxide

Uses of exothermic reactions [2]:

• hand warmers

• self-heating coffee

Uses of endothermic reactions:

• cold packs

Disposable hand warmer [2]

• iron + sodium chloride --> iron (III) oxide

• lasts for hours

Reusable hand warmer [5]

• often sodium ethanoate (CH3COO-Na+)

• supersaturated solution of dissolved salt

• crystallises when metal disc is pressed

• put in boiling water to re-dissolve

• lasts about 30 minutes

Self-heating can reaction:

calcium oxide + water --> calcium hydroxide

Instant cold packs [3]

• ammonium nitrate and water

• when dissolved, takes in energy

• lasts about 20 minutes