Internal energy and absolute zeroEdexcel International A Level Physics: Mind map

Exam questions on Internal energy and absolute zero

1. A 0.20 kg block of ice at 0 °C is placed in a warm room. It absorbs energy from the air, melts completely and forms water that is still at 0 °C. A physics class is asked to describe what has changed for the molecules in the sample.
   Explain why the temperature of the sample does not change while the ice is melting, although it is absorbing energy.2 marks
2. A cryogenics laboratory stores liquid nitrogen, which boils at 77 K, and uses it to cool samples. Technicians compare the behaviour of nitrogen molecules at the temperature of the cold store with their behaviour at room temperature, 300 K.
   A technician says that absolute zero is the temperature at which the molecules have no energy at all. Explain what is meant by absolute zero in terms of the molecules, correcting the statement if necessary.2 marks
3. A sealed, rigid flask contains a fixed mass of gas that behaves as an ideal gas. At 27 °C the internal energy of the gas is 1.5 kJ. The flask is then heated until the gas is at 327 °C.
   Calculate the ratio of the mean kinetic energy of the molecules at 327 °C to that at 27 °C.3 marks