Question

Based on the first law of thermodynamics, which one of the following is correct?

• A. For an isochoric process= $\Delta E=-Q$
• B. For an adiabatic process= $\Delta E=-W$
• C. For an isothermal process= $Q=+W$
• D. For a cyclic process= $Q=-W$

Answer 1

Answer: (D)

The mathematical equation for first law of thermodynamics is,
$\Delta E=Q+W$
(a) For isochoric process, $\Delta V=0$
$W=-P_{ext}\Delta V=0$
$\therefore $ $\Delta E=Q$
(b) For adiabatic process, $Q=0$
$\Delta E=W$
(c) For isothermal process, $\Delta T=0$
and $\Delta E=0$
$Q=-W$
(d) For cyclic process, state functions like
$\Delta E=0$
$Q=-W$