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2 marksFirst Law of Thermodynamics

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

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.

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 this case?

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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)(v)Deduce the value of C_p, the molar heat capacity of the gas, at constant pressure.[2 marks]

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