Question

The first law of thermodynamics takes the form $W=-\Delta H$ when applied to

• A. A closed system undergoing a reversible process
• B. open system undergoing an adiabatic process with negligible changes in kinetic and potential energies
• C. A closed system undergoing a reversible constant volume process
• D. A closed system undergoing a reversible constant pressure process.

Answer 1

The correct option is B open system undergoing an adiabatic process with negligible changes in kinetic and potential energies

(b)
The first law of thermodynamics takes the form $W=-\Delta H$ when applied to an open system undergoing an adiabatic process with negligible changes in kinetic and potential energies.

$H_1+\frac{1}{2}m{C}_1^2+mg{z}_1+Q$
$=H_2+\frac{1}{2}m{C}_2^2+mg{z}_2+W$
$H_1=H_2+W$
$-(H_2-H_1)=W$
$W=-\Delta H$