Why heat is a path function and not state function.?

Question

I need to understand this as to why heat (also work) are considered path function. How do they have inexact integral? Kindly some one explain

Answer 1

Heat (work) is a path function because how you move from one state to another determines the work done on or by the system. Thus, heat can't be a state function. For instance, if a gas expands isothermally, then heat has to be supplied to the system so that the gas maintains its temperature as it expands. But if you do this adiabatically, then the system does work. Same final state (pressure and volume) bt different work and heat.

Answer 2

Is Heat A State Function

Answer 3

The state of a substance can be determined uniquely by the pressure, volume and temperature.

Even, if any one of the three quantities changes, the state of the substance change.


If the volume remains the same, the path of the change is called isochoric change.

If the pressure remains the same, the path of the change is called isobaric change.

If the temperature remains the same, the path of the change is called isothermal change.


In all the above three process, there is heat exchange from the surroundings.

Depending upon the path along which the states are connected we can always determine the exchange of heat. Heat is a function of path for all the above process.

If the three parameters vary, then there are two conditions. One in which there is always heat exchange and another there is no heat exchange at all.

In the former case, the states can be represented by the three parameters and heat exchange is involved along the curve joining the states and is not depended upon the states.

In the latter case, there is no heat exchange at all and is called adiabatic change.

Thus there are states with out the involvement of heat.

Hence considering all possibilities the states are represented only by the three parameters and not by heat.

However, heat is involved and it is a function of path and not a function of state.
Let the state of the substance be represented by (p, v,t) . When the substance is taken along a curve of different states and brought back to its initial state, the three parameters will return to the original state.


But the heat which is a function of the path do not cancel while competing a closed circuit showing that the integral is not exact.

Answer 4

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