In a particular reaction ' $x$ ' kJ of heat is released by the system and ' y ' kJ of work done is done on…
In a particular reaction ' $x$ ' kJ of heat is released by the system and ' y ' kJ of work done is done on the system. What is internal energy change?
$\mathrm{x}-\mathrm{ykJ}$
$\mathrm{y}-\mathrm{xkJ}$
$\mathrm{x}+\mathrm{ykJ}$
xy kJ
Solution
$\mathrm{Q}=-\mathrm{xkJ}, \mathrm{~W}=+\mathrm{ykJ}$
According to the first law of thermodynamics,
$\begin{array}{ll}
\therefore \Delta U =Q+W \\
\Delta U =-x+y k J=y-x k J
\end{array}$