zz Distinguish between endothermic and exothermic chemical reactions.
Produce an energy profile diagram for endothermic and exothermic reactions.
Some chemical reactions give out heat. These are exothermic reactions. In exothermic reactions, heat energy is given out by the reacting chemicals to the surroundings so that the temperature increases.
Examples of exothermic reactions include: z z
z z
Coal burning to heat a room. Fireworks exploding.
Other chemical reactions take in heat energy from the surroundings, causing a decrease in temperature. These are called endothermic reactions.
z Fig. 12.2.1
Coal burning is an exothermic reaction
Examples of endothermic reactions include: zz
Sherbet on your tongue. zz Using an instant cold pack to reduce swelling.
Exothermic = energy out (temperature increases in reaction mixture, i.e. in the beaker)
Endothermic = energy in (temperature decreases in reaction mixture, i.e. in the beaker)
z
Fig. 12.2.2
The endothermic reaction that takes place in an instant cold pack quickly lowers its temperature
z Remembering chemical reactions
Here is an easy way to remember the difference between exothermic and endothermic reactions: zz
z z 206 206
Endothermic reactions: energy enters the reaction. Exothermic reactions: energy exits the reaction.
