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 $=20.8Jmo{l}^{-1}{K}^{-1}$

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

Answer 1

Answer: (D)

$\because$ Given, Molar heat capacity for oxygen
$=20.8Jmo{l}^{-1}{K}^{-1}$
$Q=nC\Delta T$
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 $\Delta U=60\times 20.8=1248J$