Thermodynamics Question 4
Question 4 - 29 January - Shift 2
Which of the following relations are correct? (A) $\Delta U=q+p \Delta V$
(B) $\Delta G=\Delta H-T \Delta S$
(C) $\Delta S=\frac{q _{rev}}{T}$
(D) $\Delta H=\Delta U-\Delta nRT$
Choose the most appropriate answer from the options given below : (1) C and D only
(2) B and C only
(3) A and B only
(4) B and D only
Show Answer
Answer: (2)
Solution:
Formula: Heat capacity
Only (B) and (C) are correct.
(B) $G=H-TS$
At constant $T$
$\Delta G=\Delta H-T \Delta S$
(A) First law is given by
$\Delta U=Q+W$
If we apply constant $P$ and reversible work.
$ \Delta U=Q-P \Delta V $
(C)By definition of entropy change
$ dS=\frac{dq _{rev}}{T} $
At constant $T$
$ \Delta S=\frac{q _{rev}}{T} $
(D) $H=U+PV$
For ideal gas
$H=U+nRT$
At constant $T$
$ \Delta H=\Delta U+\Delta nRT $
