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

$(a)\;4\;RT\qquad(b)\;15\;RT\qquad(c)\;9\;RT\qquad(d)\;11\;RT$

Answer : $\;11\;RT$
Explanation :
$U= \large\frac{n_{1}f_{1}}{2}$$RT + \large\frac{n_{2}f_{2}}{2}$$RT$
f - No.of degrees of freedom
$f_{1}\;$ for a diatomic gas = 5
$f_{2}\;$ for a monoatomic gas =
Therefore , $\;U=\large\frac{2 \times 5}{2} $$RT+ \large\frac{4\times 3}{2}$$RT$
$= 11 RT$
edited Aug 9, 2014