Energy Changes in Chemistry

Question 1

Examples of exothermic reactions

Answer 1

Neutralisation - acid + alkali - salt + water.
Displacement reactions - e.g. copper + silver nitrate - copper nitrate + silver.
Combustion.
Oxidation.

Question 2

Examples of endothermic reactions

Answer 2

Thermal decomposition - break down of a substance using heat.
Cracking - process of breaking large hydrocarbon molecules into a mixture of smaller ones.
Electrolysis.
Photosynthesis.

Question 3

What happens in an exothermic reaction?

Answer 3

The temperature rises as heat is released to the surroundings.
An exothermic reaction had a negative energy change value because energy is lost from the reaction.

Question 4

What happens in an endothermic reaction?

Answer 4

The temperature decreases as heat is taken in from the surroundings. An endothermic reaction has a positive energy change as energy has to be added to the reaction.

Question 5

What type of reaction is bond making and bond breaking?

Answer 5

Making - exothermic
Breaking - endothermic

Question 6

How to calculate energy change in a reaction?

Answer 6

Break - make = energy change

Question 7

What is bond energy?

Answer 7

The amount of energy required to break one mole of a specific covalent bond. The higher the bond energy the stronger the bond.