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1 markFirst Law of Thermodynamics

CAPE Physics Unit 1 · 2008 · Paper 2 · Question 6(a)(ii)

The first law of thermodynamics is given by the equation ΔU = Q + W.

Use the first law of thermodynamics to explain why the molar heat capacity at constant pressure, Cₚ, is greater than the molar heat capacity at constant volume, Cᵥ.

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Other parts of this question

  1. 6(a)The first law of thermodynamics is given by the equation ΔU = Q + W.[1 mark]
  2. 6(a)(i)Explain the meaning of EACH of the terms used in the equation when the law is applied to the heating of a fixed mass of gas.[6 marks]
  3. 6(b)One mole of an ideal monatomic gas, Cᵥ = (3/2)R, is taken through the cycle represented by states 1 to 4 as shown in Figure 6. Assume that at state 1, P₁ =…[1 mark]
  4. 6(b)(i)the work done during the cycle[9 marks]
  5. 6(b)(ii)the temperature T₂ at state 2[1 mark]
  6. 6(b)(iii)the energy added as heat during the processes 1 → 2 and 2 → 3[1 mark]
  7. 6(b)(iv)the efficiency of the cycle.[1 mark]

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