Question

If the value of $C_p$ for nitrogen gas is $j{K}^{-1}mo{l}^{-1}$, then the value of $\Delta H$ on heating $28g$ 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 :
$C_p=7J{K}^{-1}mo{l}^{-1}$
Weight of $N_2$ gas $=28gm$
$T_1=0^{\circ }C=273+0=273K$
$T_2=100^{\circ }C=273+100=373K$
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
$\Delta H=nCp(T_2-T_1)$
$=2\times 7(373-273)$
$=14\times 100=1400\text{ Joule }$