Question

Consider the following thermodynamic properties:
(i) work done on a system; (ii) heat absorbed; (iii) entropy; (iv) enthalpy.
Which of these properties are state functions?

(a) (i) and (ii) only
(b) (i) and (iii) only
(c) (i) only
(d) (iii) and (iv) only

Answer 1

d is the answer (Explaination is given in the following section)

WORK DONE

Work done on a system is different for different processes. It can clearly be seen from the following expression

Work done in case of an Isothermal process is

.........(1)

n is number of moles

R is universal gas constant

T is temperature of the system

is the final volume of the system

is the Initial volume of the system

In case of Adiabatic process work done is given by

........(2)

Here is Initial pressure of the thermodynamic system and is ratio of specific heats

Obviously expression 1 and 2 are different that says work done depends on the path. So, it is clear that work done is not a state function

HEAT ABSORBED

From First law of thermodynamics, Heat absorbed by the system is utilised in doing the external work and increasing the internal energy of the system. Since heat absorbed depends on work done which is path dependent function (Meaning: it doesn't depend on the initial and final states of the system). Work done is not a state function.

ENTROPY

The entropy is state function, it is defined as a an amount of disorderness present in the system. Unlike workdone and heat absorbed, Entropy depends on the initial and final states of the thermodynamic system.

ENTHALPY

Enthalpy is one of the thermodynamic potentials. The mathematical form is given below

Here U,p and v are Internal energy, pressure and volume of the system respectively. These are all the state functions. This concludes that H is also a state function.

Hence the answer is d