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