Question

Identify the number of correct statements:
i) All adiabatic process must be fast.
ii) All reversible process must be slow.
iii) For adiabatic process, $dq=0$.
iv) For an adiabatic process, work is a path function.
v) Absolute value of internal energy can not be determined.
vi) $H=E+PV$ is applicable only for ideal gases.
vii) $\Delta H_f^{\circ }\left(D_2\right(g\left)\right)=0$, at 298 K.
viii) $\Delta G_f^{\circ }\left(H^{+}\text{aq}\right)=0$, at 298 K.
ix) Expansion of an ideal gas not always represent an increase in entropy of system.

• A. (ii), (iii), (ix), (v)
• B. (vii), (viii)
• C. (i), (vii), (v)
• D. (iv), (viii), (ix), (v)

Answer 1

Answer: (A), (B)

The correct options are
A (ii), (iii), (ix), (v)
B (vii), (viii)

(ii), (iii), (v), (vii), (viii), (ix) are correct statements.
(i)In thermodynamics, an adiabatic process is a type of thermodynamic process which occurs without transferring heat or mass between the system and its surrounding. Adiabatic processes only require insulation, it does not matter whether the process is fast or slow. Hence, statement (i) is incorrect.

(ii)All the processes taking place in the cycle of operation must be infinitely slow- is a condition for reversible processes. Hence, All reversible processes must be slow. Statement (ii) is correct.

(iii) In an adiabatic process, no heat is transferred: $dq=0$. Option (iii) is correct.

(iv) For an adiabatic process, $\Delta U=w$, since $U$ is a state function, $w$ must also be a state function. Hence, (iv) is not correct.

(v)The absolute value of internal energy of a substance cannot be determined and it is not required as well. We only need change in internal energy and change in internal energy can be determined. Hence, option (v) is correct.

(vi)$H=E+PV$ is applicable to all types of gases. Hence, option (vi) is incorrect.

(vii) All elements in their standard states have a standard enthalpy of formation zero Since, $D_2$ is gas in its standard state.Hence, it’s standard enthalpy of formation is zero.

(viii) Similar to (vii), $H^{+}$ ion is found in nature in aqueous state. Hence, standard free energy change in formation of $H^{+}$ ion is zero

(ix) Reversible expansion of an ideal gas in an adiabatic process has zero entropy change. Hence, expansion of an ideal gas does not always represent an increase in entropy of the system.