5 moles of unknown gas is heated at constant volume from 10 °C to 20 °C. The molar specific heat of this gas at constant pressure cp = 8 cal/mol.°C and R = 8.36 J/mol.°C. The change in the internal energy of the gas is calorie.
300
R = 8.364.18 = 2 cal/mol °C ∵ 1 cal = 4.18 J
Mayer's relation: cv = cp - R = 8 - 2 = 6 cal/mol °C
U = ncv T (true for any process of an ideal gas)
U = 5 6 (20 - 10) = 300 cal
Answer: 300
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