7 3 (a) State what is meant by the internal energy of a system. ..[2] (b) Explain, by reference to work done and heating, whether the internal energy of the following increases, decreases or remains constant: (i) the gas in a toy balloon when the balloon bursts suddenly, ...[3] (ii) ice melting at constant temperature and at atmospheric pressure to form water that is more dense than the ice. ... [3] [Total: 8]