C2- exothermic and endothermic reactions

Question 1

What do exothermic reactions do?

Answer 1

Exothermic reactions transfer energy to the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to become hotter.

Question 2

What are some examples of exothermic reactions?

Answer 2

Combustion (burning)
Many oxidation reactions, for example rusting
Neutralisation reactions between acids and alkalis

Question 3

What are some uses of exothermic reactions?

Answer 3

Exothermic reactions can be used for everyday purposes. For example, hand warmers and self-heating cans for drinks (such as coffee) use exothermic reactions.

Question 4

What are endothermic reactions?

Answer 4

These are reactions that take in energy from the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to get colder.

Question 5

What are some examples of endothermic reactions?

Answer 5

Electrolysis
The reaction between ethanoic acid and sodium carbonate
The thermal decomposition of calcium carbonate in a blast furnace

Question 6

What are some uses of endothermic reactions?

Answer 6

Endothermic reactions can be used for everyday purposes. For example, certain sports injury cold packs use endothermic reactions.

Question 7

If something decomposes, what is the reaction that happens?

Answer 7

endothermic - energy must be transferred from the surroundings for it to happen.

Question 8

Describe the decomposition of ammonium chloride

Answer 8

Ammonium chloride decomposes when it is heated, so the forward reaction is endothermic - energy must be transferred from the surroundings for it to happen. The backward reaction is exothermic - energy is transferred to the surroundings when it happens.

Question 9

Describe the reaction between anhydrous copper sulfate and water

Answer 9

Water is driven off from hydrated copper sulfate when it is heated, so the forward reaction is endothermic - energy must be transferred from the surroundings for it to happen. The backward reaction is exothermic - energy is transferred to the surroundings when it happens. This is easily observed. When water is added to anhydrous copper sulfate, enough heat is released to make the water bubble and boil.