Chapter 5: Thermochemistry

Chapter 5



Topic 5.1

Endothermic And Exothermic
Reactions

Endo --- thermic
(Absorb) (heat energy)

Endothermic reaction
= a chemical reaction that absorbs heat from the surrounding

Heat absorption is more than heat release

Energy change:
Heat energy → Chemical energy

Will cause the surrounding temperature to decrease

Examples of reaction:

1. Photosynthesis
2. Boiling
3. Evaporation
4. Cooking

Exo --- thermic
(Release) (heat energy)

Exothermic reaction
= a reaction that releases heat into the surrounding

Heat release is more than heat absorption

Energy change:
Chemical energy → Heat energy

Causes the surrounding temperature to increase

Examples of reaction:

1. Respiration
2. Rusting of iron
3. Burning of fuel in excess oxygen
4. Reaction between an acid with an alkali
5. Decomposition

Device used to measure energy change:

THERMOMETER

Experiment: Textbook page 149 – 151

Aim:
Compare and contrast the exothermic and endothermic
reactions

Procedure:
Refer to page 150 – follow accordingly!

Textbook page 158

Modify and make an instant hot pack:
1. Fill the thick plastic bag with calcium chloride.
2. Fill the thin plastic bag with water and seal it.
3. Place the plastic bag filled with water into the thick plastic bag.
4. Poke a small hole on the bag filled with water.
5. Seal the thick plastic bag.
6. Squeeze the hot pack.

What will happen?
Water will seep out from the thin plastic bag and reacts with the salt in
the thick plastic bag, temperature increases, pack becomes HOT! (≈ 60°C)



Uses:

When doing vigorous activity over a long period, muscles
become painful or cramped due to the production and
accumulation of lactic acid.

Hot pack can dilate the blood capillary so that blood flows
faster to remove acid lactic. Pain or muscle cramps can be
reduced.

Textbook page 158

Modify and make an instant cold pack:
1. Fill the thick plastic bag with ammonium nitrate.
2. Fill the thin plastic bag with water and seal it.
3. Place the plastic bag filled with water into the thick plastic bag.
4. Poke a small hole on the bag filled with water.
5. Seal the thick plastic bag.
6. Squeeze the hot pack.

What will happen?
Water will seep out from the thin plastic bag and reacts with the salt in the
thick plastic bag, temperature decreases, pack becomes COLD! (≈ 16°C)



Uses:
Relief fever (remove heat)
Constricts the blood capillary to reduce bleeding.