(a)[2]
State two ways in which the first law of thermodynamics shows that a system’s internal energy may change.
(b(i))[3]
Use the first law of thermodynamics to explain why a bicycle pump becomes hot when it is used to inflate a tyre quickly.
(b(ii))[3]
With reference to molecular energies, explain why the temperature of water stays at $100\,^\circ\text{C}$ as it vaporises in a kettle, even though it is still being heated.