Question

One mole of oxygen is heated at constant pressure starting at 0°C. How much heat energy in cal must be added to the gas to double its volume ? Take R = 2 {(cal) / (mole)} 

(A) 1938 

(B) 1920 

(C) 1911 

(D) 1957

Answer 1

Correct option: (C) 1911

Explanation:

n = 1

Oxygen is diatomic hence C_p = (7/2)R

Volume is doubled as constant pressure

∵ PV = nRT

V = [(nRT) / P]

As P is constant, V ∝ T

Hence energy = Q = n C_P ΔT

= 1 × (7/2) × 8.31 × (2T₁ – T₁)

= (7/2) × 8.31 × 273….as T₁ = 273K

= 8000J = [(8000) / (4.18)]cal = 1911 cal