Question

A gas mixture consists of $2mol$ of oxygen and $4mol$ of argon at temperature $T$. Neglecting all vibrational modes, the total internal energy of the system is

• A. $4RT$
• B. $15RT$
• C. $9RT$
• D. $11RT$

Answer 1

Answer: (D)

$11RT$

$O_2$ molecule has 3 translational and 2 rotational degrees i.e total of 5 degrees of freedom.
Since Argon is a noble gas, it consists only of atoms and the energy is purely translational kinetic energy.
Total internal energy: $U=2\times \frac{5}{2}RT+4\times \frac{3}{2}RT=11RT$