Physics_7408 Question Paper 2.

Physics_7408 Question Paper 2. Answer all questions in this section. 0 1 Figure 1 shows a perfectly insulated cylinder containing 0.050 kg of liquid nitrogen at a temperature of 70 K. A heater transfers energy at a constant rate of 12 W to the nitrogen. A piston maintains the pressure at 1.0 × 105 Pa during the heating process. Figure 1 Do not write outside the box 3 *03* Turn over ► Do not write outside the 0 1 box . 1 The nitrogen is heated from 70 K and is completely turned into a gas after 890 s. Calculate the specific heat capacity of liquid nitrogen. Give an appropriate unit for your answer. specific latent heat of vaporisation of nitrogen = 2.0 × 105 J kg−1 boiling point of nitrogen = 77 K [5 marks] specific heat capacity = unit = Question 1 continues on the next page 4 *04* Do not write outside the 0 1 box . 2 The work done by the nitrogen in the cylinder when expanding due to a change of state is X. The energy required to change the state of the nitrogen from a liquid to a gas is Y. Deduce which is greater, X or Y. density of liquid nitrogen at its boiling temperature = 810 kg m−3 density of nitrogen gas at its boiling temperature = 3.8 kg m−3 [4 marks] 9 5 *05* Turn over ► Do not write outside the 0 2 box . 1 State what is meant by the internal energy of a gas. [2 marks] 0 2 . 2 Absolute zero of temperature can be interpreted in terms of the ideal gas laws or the kinetic energy of particles in an ideal gas. Describe these two interpretations of absolute zero of temperature. [2 marks] Question 2 continues on the next page 6 *06* Do not write outside the box 0 2 . 3 A mixture of argon atoms and helium atoms is in a cylinder enclosed with a piston. The mixture is at a temperature of 310 K. Calculate the root mean square speed (crms) of the argon atoms in the mixture. molar mass of argon = 4.0 × 10−2 kg mol−1 [3 marks] crms = m s−1 0 2 . 4 Compare the mean kinetic energy of the argon atoms and the helium atoms in the mixture. [1 mark] 0 2 . 5 Explain, in terms of the kinetic theory model, why a pressure is exerted by the gas on the piston. [3 marks] 7 *07* Turn over ► Do not write outside the box 0 2 . 6 The mixture of gases in the cylinder stays the same. Explain, using the kinetic theory model, two changes that can be made independently to reduce the pressure exerted by the gas. [3 marks]