Question

2.2 g of nitrous oxide (N2O) gas is cooled at a constant pressure of 1 atm from 310 K to 270 K causing the compression of the gas from 217.1 mL to 167.75 mL. The change in internal energy of the process, ΔU is '-x' J. The value of 'x' is ____. [nearest integer]
(Given : atomic mass of N = 14 g mol-1 and of O = 16 g mol-1
Molar heat capacity of N2O is 100 J K-1 mol-1)

Answer 1

$T_1$ = 310K , $T_2$ = 270K
$ΔT = T_2 - T_1$ = 270K - 310K = -40K
qp = n Cp ΔT
$= \frac{2.2}{44} × 100 × (-40)$
= -200 J
$ΔV = V_2 - V_1$= (167.75 - 217.1) mL
= 49.35 mL
w = -Pext × DV
w = -(1) × $( \frac{-49.35}{1000})$ atm L
w = + 0.04935 ×101.3 J
w = 4.99 J ∼ 5 J
ΔU = q + w
= - 200 + 5
= -195 J
So, the value of x is 195.