Energy Changes

Question 1

Explain how a catalyst increases the rate of the reaction. [2]

Answer 1

• provides an alternative route

- with a lower activation energy

Question 2

Explain why, in terms of the energy involved in bond breaking and bond making, the combustion of methane is exothermic. [3]

Answer 2

energy is taken in / required to break bonds [1]
energy is given out when bonds are made [1]
the energy given out is greater than the energy taken in [1]

Question 3

Write an equation for the reaction of hydrogen with oxygen

Answer 3

2H₂ + O₂ –> 2H₂O

Question 4

Name the advantages of hydrogen fuel cells

Answer 4

Do not need to be electrically recharged

No pollutants are produced

Question 5

Name the disadvantages of hydrogen fuel cells

Answer 5

Hydrogen is highly flamable
Hydrogen is sometimes produced from non-renewable sources such as natural gas
Hydrogen is difficult to store

Question 6

Write the two half equations for a hydrogen fuel cell

Answer 6

2H₂ + 4OH^- –> 4H₂) + 4e^-
O_{2 + 2H2O + 4e^- –> 4OH^-}