Question

140 gm of nitrogen absorbs 60 calories of heat without change in volume. If the temperature increases from 27°C to 30°C while doing so, then what is the value of molar heat capacity ?

(a) 2 cal K^-1 mol^-1

(b) 4 cal K^-1 mol^-1

(c) 5 cal K^-1 mol^-1

(d) 20 cal K^-1mol^-1 

Answer 1

Correct option  (b) 4 cal K^-1 mol^-1

Explanation:

As the gas absorbs heat without change in volume, W = 0 (since, ΔV = 0)

Heat absorbed, q = 60 cal, Since ΔE = q + W

= 60 + 0 = 60 cal; C_v = ΔE/(T₂ – T₁ ) = 60/(303 – 300) = 20 cal K^–1

Since moles of N₂ gas given

= 140/28 = 5,

Molar heat capacity

= 20/5 cal K^–1 = 4 cal K^–1 mol^–1