Energy changes

Question 1

Compare hydrogen fuel cells to rechargeable batteries(4)

Answer 1

• Do not get less efficient the longer they run
  -Less/no toxic chemicals to dispose of
  -Can be renewable but hydrogen is often made from fossil fuels so more pollution
  -Hydrogen is highly (flammable and) explosive and so difficult to store safely

Question 2

Give the equation at the negative electrode (anode) of a hydrogen cell.

Answer 2

H2 ⟶ 2H+ + 2e-

Question 3

Give the equation at the positive electrode (cathode) of a hydrogen cell.

Answer 3

O2 + 4 H+ + 4 e- ⟶ 2 H2O

Question 4

Give the overall equation of a hydrogen cell.

Answer 4

2H2 +O2 →2H2O

Question 5

How do hydrogen fuel cells work?

Answer 5

Hydrogen is oxidised and water (and electricity) is produced.

Question 6

Why can alkaline (non-rechargeable) batteries not be recharged?

Answer 6

Their reaction is not reversible.

Question 7

Why do non-rechargeable cells stop producing electricity?

Answer 7

One of the reactants is used up so the reaction stops.

Question 8

Give 2 reasons why a hydrogen fuel cell is seen as non polluting.

Answer 8

• Only water is produced which is harmlessand renewable
• CO2 is not produced

Question 9

RPA 4: what are 3 improvements for accuracy?

Answer 9

• Use a polystyrene cup and lid to reduce energy transfers to surroundings
• Stir more so all particles react
• Use a digital thermometer as measures to a higher degree of accuracy

Question 10

Give two effects of atmospheric pollution which are reduced by using catalytic converters

Answer 10

• acid rain
• global dimming (soot)

Question 11

RPA 4: Suggest why a polystyrene cup is used rather than a glass beaker

Answer 11

Polystyrene is a better insulator so reduces heat energy loss to the surroundings

Question 12

Explain the difference between processes in electrolysis and a chemical cell

Answer 12

Electrolysis uses electricity to produce a chemical reaction whereas a chemical cell uses a chemical reaction to produce electricity

Question 13

What is required for particles to react?

Answer 13

Particles must collide with sufficient energy

Question 14

Explain why a reaction releases energy to the surroundings.

Answer 14

Energy is needed to break bonds and energy is released when bonds form. More energy is released than absorbed.

Question 15

Name the type of reaction that takes place when dilute HCl reacts with a metal

Answer 15

Exothermic neutralisation reaction