Question

If the value of $C_{p}$ for nitrogen gas is $j K ^{-1} mol ^{-1}$, then the value of $\Delta H$ on heating $28 \,g$ of nitrogen gas from $0^{\circ} C$ to $100^{\circ} C$ at constant pressure will be :

• A. 1200 J
• B. 1300 J
• C. 1400 J
• D. 1500 J

Answer 1

Answer: (C)

Given that :
$C_{p}=7 JK ^{-1} mol ^{-1}$
Weight of $N _{2}$ gas $=28\, gm$
$T_{1}=0^{\circ} C =273+0=273\, K$
$T_{2}=100^{\circ} C =273+100=373\, K$
Now, by using :
Number of moles
$=\frac{\text { Weight of } N _{2}}{\text { Molecular weight of } N _{2}}$
$=\frac{28}{14}=2$
Now, by using
$\Delta H = nCp (T_2 - T_1) $
$ = 2\times 7(373-273)$
$=14 \times 100=1400 \text { Joule }$