Question

The change in internal energy when $\text{5}$ mole of hydrogen is heated to $20^{^\circ } \text{C}$ from $10^{^\circ } \text{C}$ is $\left(\right.$ specific heat of hydrogen at constant pressure is $8$ cal $\left(\text{mol} ^\circ \text{C}\right)^{- 1}$ $\left.$

• A. $\text{200}$ cal
• B. $\text{350}$ cal
• C. $\text{300}$ cal
• D. $\text{475}$ cal

Answer 1

Answer: (C)

$C_{p}=8$ cal $\left(m o l ℃\right)^{- 1}, \, C_{v}=C_{p}-R=8-2=6$ cal $\left(m o l \, ℃\right)^{- 1}$
$dU=mC_{v}\left(T_{2} - T_{1}\right)=5\times 6\left(20 - 10\right)=300 \, cal$