Question

When a system is taken from state $a$ to state $b$ along the path $a-c-b,60J$ of heat flows into the system and $30J$ of work is done by the system. Along the path $a-d-b$, if the work done by the system is $10J$, heat flow into the system is

• A. $6J$
• B. $12J$
• C. $18J$
• D. $40J$

Answer 1

The correct option is D $40J$

$Q_{acb}=\Delta U_{acb}+W_{acb}$
$Q_{bda}=\Delta U_{bda}+W_{bda}$
$Q_{acb}+Q_{bda}=(\Delta U_{acb}+\Delta U_{bda})+W_{acb}+W_{bda}$
$\Delta U_{acb}+\Delta U_{bda}=0$
$\Rightarrow 60+Q_{bda}=30-10$
$Q_{bda}=-40J$
$Q_{adb}=40J$