Question

When an ideal monoatomic gas is heated at constant pressure, the fraction of the heat energy supplied which increases the internal energy of the gas is

• A. 2/5
• B. 3/5
• C. 3/7
• D. 5/7

Answer 1

Answer: (B)

By first law of thermodynamics
Q = U + W
$=\frac{f}{2}nRT+P\int dV=\frac{f}{2}nRT+PV$
or$Q=\frac{f}{2}nRT+nRT\left(\because PV=nRT\right)$
$=\frac{3}{2}nRT+nRT=\frac{5}{2}nRT$
$\therefore$ Fraction of heat energy supplied $=\frac{U}{Q}$
$=\frac{\left(3/2\right)nRT}{\left(5/2\right)nRT}=\frac{3}{5}$