Question

How much heat energy should be added to the gaseous mixture consisting of $1g$ of hydrogen and $1g$ of helium to raise its temperature from $0^{o}C$ to ${100}^{o}C$. At constant pressure ($R=2cal/molK$)?

• A. $475cal$
• B. $295cal$
• C. $350cal$
• D. $345cal$

Answer 1

The correct option is A $475cal$

Hydrogen is diatomic. Hence its $C_p=C_{p_1}=3.5R$
Helium is monoatomic. Hence its $C_p$=$C_{p_2}=2.5R$
Thus heat required, $\Delta Q$ $=(n_1{C}_{p_1}+n_2{C}_{p_2})\times$ $\Delta T$
Here, $n_1=$ number of moles of hydrogen $=0.5$

$n_2=$ number of moles of helium $=0.25$

$\Delta T=$ change in temperature $=100K$
Hence, $\Delta Q=475cal$