Question

How much heat energy in joules must be supplied to $14gms$ of nitrogen at room temperature to rise its temperature by ${40}^{o}C$ at constant pressure?
(Mol.wt.of $N_2=28gm,R=constant$)

• A. $50R$
• B. $60R$
• C. $70R$
• D. $80R$

Answer 1

Answer: (C)

$70R$

Given,

Mass of nitrogen, $m=14gms$

Temperature, $T={40}^{0}C$

Molecular weight of nitrogen, $M=28gms$

Now,

We know that,

Amount of heat supplied, $Q=n{C}_p\left(dT\right)$

No, of moles, $n=\frac{m}{M}$

$\therefore Q=\frac{m}{M}{C}_{p}dT$

$\begin{array}{c}=\frac{14}{28}\times \frac{7R}{2}\times 40\\ =70R\end{array}$

Hence,

Option $C$ is correct answer.