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 $