c7 - energy changes

Question 1

define exothermic reactions

Answer 1

reactions that transfer energy to the surroundings

Question 1

what happens when chemical reactions take place?

Answer 1

energy is transferred as bonds are broken and made.

Question 2

give three examples of exothermic reactions

Answer 2

• combustion (burning fuels)
• oxidation reactions, e.g respiration
• neutralisation reactions, involving acids and bases

Question 3

what is a key feature in exothermic reactions?

Answer 3

products have less energy content than reactions

Question 4

define endothermic reactions

Answer 4

take in energy from surroundings

Question 5

what is a key feature in endothermic reactions?

Answer 5

• products have more energy content than reactants
• some endothermic reactions cause a decrease in temperature and others require a supply of energy to keep the reaction going

Question 6

give an example of endothermic reaction

Answer 6

thermal decomposition reactions

Question 7

how can you investigate energy changes in reactions involving at least one solution?

Answer 7

record initial temperatures of any solutions and the maximum or minimum temperature reached in the course of the reaction

Question 8

what can exothermic reactions be used for?

Answer 8

heating things
e.g: hand warmers, self-heating cans
- in some hand warmers and cans the reactants are used up and so cannot be used again

Question 9

give an advantage and a disadvantage of a reusable handwarmer

Answer 9

advantage: can be reused
disadvantage: heat only lasts around 30 mins

Question 10

give an advantage and a disadvantage of a single-use handwarmer

Answer 10

advantage: can be used for hours
disadvantage: goes to waste ones used once

Question 11

what can endothermic reactions be used for?

Answer 11

used to cool things
e.g: chemical cold packs containing ammonium nitrate and water