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Which of the following are not state functions ?
(I) $q + w$
(II) $q$
(III) $w$
(IV) $H - TS$
(I) $q + w$
(II) $q$
(III) $w$
(IV) $H - TS$
A
(I), (II) and (III)
B
(II) and (III)
C
(I) and (IV)
D
(II), (III) and (IV)
Detailed Solution
State functions or state variables depend only on the state of the system and not on the path by which that state is reached.
Here '$w$' represents work done and '$q$' represents the amount of heat. Both depend on the path followed, so both of these are not state functions (they are path functions).
(I) $q + w = \Delta U$, the change in internal energy (first law of thermodynamics). Internal energy is a state function, so $q + w$ is a state function even though $q$ and $w$ separately are not.
(IV) $H - TS = G$, the Gibbs free energy. $H$, $T$ and $S$ are all state functions, so $G$ is also a state function.
Therefore the quantities that are not state functions are (II) $q$ and (III) $w$.
Here '$w$' represents work done and '$q$' represents the amount of heat. Both depend on the path followed, so both of these are not state functions (they are path functions).
(I) $q + w = \Delta U$, the change in internal energy (first law of thermodynamics). Internal energy is a state function, so $q + w$ is a state function even though $q$ and $w$ separately are not.
(IV) $H - TS = G$, the Gibbs free energy. $H$, $T$ and $S$ are all state functions, so $G$ is also a state function.
Therefore the quantities that are not state functions are (II) $q$ and (III) $w$.