Question

70 calorie of heat are required to raise the temperature of 2 mole of an ideal gas at constant pressure from 30°C to 35°C. The amount of heat required to raise the temperature of the same gas through the same range at constant volume is .................. calorie. 

(A) 50 

(B) 30 

(C) 70 

(D) 90

Answer 1

Correct option: (A) 50

Explanation:

ΔQ = n ∙ C_P ∙ ΔT…..as gas is heated at constant pressure from given data, n = 2 moles & ΔQ = 70 cal

∴  70 = 2 × C_P × (35 – 30)

∴  C_P = 7 cal/g mol/°C

As C_p – C_v = R

∴ C_v = C_p – R = 7 – 2 = 5 cal/g mol/°C

∴ as ΔQ = n C_V ΔT……To heat gas at constant volume

∴    ΔQ = 2 × 5 × (35 – 30) = 50 cal