Question

What will be the $\Delta U$ value, when one mole of oxygen $\left(O_{2}\right)$ is going from $-20^{\circ}$ to $40^{\circ} C$ at constant volume?
(Molar heat capacity for oxygen $=20.8 \,J\,mol ^{-1}\, K ^{-1}$

• A. $2496 \,J$
• B. $20.8 \,J$
• C. $416\, J$
• D. $1248 \,J$

Answer 1

Answer: (D)

$\because$ Given, Molar heat capacity for oxygen
$=20.8 \,J \,mol ^{-1} \,K^{-1}$
$Q=n C \Delta T$
where, $Q=$ value of $\Delta U$ in $J$
$n=$ number of moles $(=1)$
$C=$ heat capacity
$\Delta T=$ temperature
$Q=1 \times 20.8 \times 60$
Thus, $\Delta T=(-) 20$ to $(+) 40=60^{\circ} C$
Hence, for one mole of oxygen,
value of $\Delta U=60 \times 20.8=1248 \,J$