C5

Question 1

Exothermic réactions

Answer 1

Release energy - get hot
E.g.
Combustion
Respiration
Neutralisation 
Dissolving acids
Dissolving alkalis 
Rusting

Question 2

Endothermic reactions

Answer 2

Absorb energy - get cold.
E.g.
Thermal decomposition
Photosynthesis 
Action of light on silver bromide 
Dissolving ionic salts

Question 3

Making and breaking chemical bonds

Answer 3

Breaking = an endothermic process.
Making = an exothermic process.

Question 4

Energy changes during reactions

Answer 4

Chemical change = bonds are broken.

New substances made as product bonds are formed.

Question 5

Activation energy

Answer 5

Minimum amount of energy required to get a reaction started.
Chemical reactions only happen when particles collide with sufficient energy.

Question 6

Exothermic reaction graphs

Answer 6

Products at a lower energy level than reactants.
When reactants form products, energy is transferred to the surroundings.
Temp. of surroundings increases because energy is released during the reaction.

Question 7

Endothermic reaction graphs

Answer 7

Products at a higher level than the reactants.
As reactant form products, energy is transferred from surroundings to reaction mixture.
Temp. of surroundings decreases bc energy is taken in during the reaction.