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2 marksFirst Law of Thermodynamics

CAPE Physics Unit 1 · 2007 · Paper 2 · Question 9(b)(v)

The molar heat capacity at constant volume, C_v, of a gas is the quantity of thermal energy required to raise the temperature of one mole of the gas by one kelvin without any change in volume.

Deduce the value of C_p, the molar heat capacity of the gas, at constant pressure.

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Other parts of this question

  1. 9(a)(i)a)Use the kinetic theory of gases to explain how the molecules inside a gas cylinder containing oxygen are able to exert a pressure.[3 marks]
  2. 9(a)(i)b)Use the kinetic theory of gases to explain why pumping in more oxygen increases the pressure inside it.[1 mark]
  3. 9(a)(i)c)Use the kinetic theory of gases to explain why the pressure would increase if the cylinder were left in the sun for a long time.[2 marks]
  4. 9(a)(ii)A cylinder contains 2.8 mol of oxygen at room temperature, 27°C, and the pressure inside the cylinder is 4.5 x 10⁵ Pa. The temperature rises to 47 °C when…[4 marks]
  5. 9(b)(i)Write an equation representing the first law of thermodynamics and state CLEARLY the meaning of EACH term.[2 marks]
  6. 9(b)(ii)How much thermal energy would be required to raise the temperature of 6.2 mol of a gas from 25°C to 50°C while the volume remained constant if C_v = 12.5 J K⁻¹…[3 marks]
  7. 9(b)(iii)By HOW MUCH would the internal energy of the gas change?[1 mark]
  8. 9(b)(iv)If instead, the gas were heated at constant pressure from 25°C to 50°C the thermal energy required would be 3200 J. How much work would be done by the gas in…[2 marks]

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