Thermodynamic state
Simply, it is a point of thermodynamic system or a unique condition at which a thermodynamic system can exist.
For example : 1 atm, 27 degree Celsius.
It is the condition which defined by the property of a system. For a given state, all thermodynamic property should have unique value or are fixed.
State function
The thermodynamic properties which depend only on the end states are called state function. State functions have exact differentials.
Exact differentials :
For the state variables like temperature, pressure, volume, enthalpy
etc. the process that connects the state 1 to state 2 in no way affects the
change in value of variable from state 1 to state 2. [i.e. independent of
path]. Hence, state variable are exact differentials.
The change in exact differentials is denoted by ‘d’ or Δ .
Path function
The thermodynamic properties which depend on the path and also on end states like work, heat etc. and they are called path function. Path functions have inexact differentials.
Inexact differentials :
For path variables like work, we cannot calculate work without knowing how P and V changed during the process , so that we can find the area under the curve. Hence, these variables are path dependent for their calculation. Hence, these path variables are called inexact differentials. The change of the inexact differentials is given by ‘δ’ .
For example : A to B can be infinite ways.
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