Energy Changes (Year 11) - C7

Question 1

What is an exothermic reaction

Answer 1

It is a reaction that transfers energy to the surroundings

This causes the temperature of the surroundings to go up

Question 2

What is an endothermic reaction

Answer 2

It is a reaction that transfers energy from the surroundings

This causes the temperature of the surroundings to go down

Question 3

Examples of Endothermic reactions

Answer 3

Melting and Boiling

Question 4

Examples of Exothermic reactions

Answer 4

Combustion, Rusting and Neutralisation

Question 5

What type of reaction is breaking bonds

Answer 5

Endothermic

Question 6

What type of reaction is making bonds

Answer 6

Exothermic

Question 7

What is the equation for energy change

Answer 7

Energy change = Energy of bonds broken - Energy of bonds made
If the answer is negative then the reaction is exothermic

Question 8

Why do reactions need activation energy

Answer 8

To break the bonds in the reactants

Question 9

What do fuel cells use

Answer 9

They use fuel and oxygen to produce electrical energy

Question 10

What happens in hydrogen cells

Answer 10

Hydrogen is oxidised to produce water and electricity

Question 11

What is the overall equation for hydrogen cells

Answer 11

2H 2 + O 2 = 2H20

Question 12

What are the half equations for hydrogen cells

Answer 12

2H 2 + 4OH (N) = 4H20 + 4 electrons

O2 + 2H20 + 4 electrons = 4OH (N)
(N) = negative

Question 13

What are the advantages of hydrogen fuel cells

Answer 13

No pollution
Can be used for a range of things
Don’t need to be electrically recharged

Question 14

What are the disadvantages of hydrogen fuel cells

Answer 14

Hydrogen is highly flammable
Hydrogen is difficult to store
The hydrogen used in the cells can come from non-renewable sources

Question 15

What is a battery

Answer 15

It is 2 or more cells connected together in a series

Question 16

What does the voltage of cells depend on

Answer 16

Reactivity of metals
Electrolyte
Surface area of electrons

Question 17

What is an electrolyte

Answer 17

A solution that conducts electricity e.g. NaCl

Question 18

What are electrodes

Answer 18

They are 2 different metals which react together in an electrolyte which build up a charge difference
The positive metal is called the anode
The negative one is called the cathode

Question 19

What happens in non-rechargeable batteries

Answer 19

They use irreversible reactions

Once one reactant is used up, they stop producing a charge