Question

3 moles of an ideal monoatomic gas is heated at constant pressure of one atmosphere from $0^{\circ }$C to ${70}^{\circ }$C. Then, work done by the gas is

• A. 1.74 $kJ$
• B. 0.5 $kJ$
• C. 6.98 $kJ$
• D. 11.3 $kJ$

Answer 1

The correct option is A 1.74 $kJ$

For monoatomic gas, degrees of freedom is 3
Thus, $C_v=\frac{3}{2}R$ and $C_p=\frac{5}{2}R$
$R=8.31J/mol-K$
$dQ=dU+W$
$dQ=n{C}_{p}dT=3\times \frac{5}{2}\times 8.31\times (70-0)$
$dQ=4362.75J$
$dU=n{C}_{v}dT=3\times \frac{3}{2}\times 8.31\times (70-0)$
$dU=2617.65J$
$W=4362.75-2617.65=1745.1J$
$W=1.74KJ$