# Are thermodynamic variable and state variable the same?

Kindly note that by state variable I don't mean state function, state variables are independent variable of the state function

The terms are often used interchangeably but technically a state function describes how a state variable depends on other state variables.

For example, temperature $$T$$ is a state variable which, in the case of an ideal gas, depends on other state variables by the state function which happens to be the ideal equation

$$T=\frac{Pv}{nR}$$

Thanks for answering , but i am asking about the difference between thermodynamic variable and state variable but your answer seems to tell about the difference between state variable and state function ( if i am not wrong)

As I indicated above, the terms are most of the time used interchangeably, as in the following statement from the link below:

"Thermodynamic variables (or state variables) are easily measurable macroscopic quantities used to describe the state of a thermodynamic system".

https://www.youphysics.education/thermodynamic-variables/#:~:text=Thermodynamic%20variables%20(or%20state%20variables,galaxy%2C%20or%20a%20living%20being.

But sometimes the term thermodynamic variable is used in a broader sense to include any thermodynamic quantity, such as heat and work, which are not state functions. An example is Mark Harder’s answer in the link below where he makes the following:

“Thermodynamic variables are not necessarily state variables. Temperature heat and work are not state variables”

Except for the adjective temperature for heat (which is not correct) he is correct that heat and work are not state variables. But I don’t like to use the term “thermodynamic variable” in connection with heat and work. I would prefer something like “thermodynamic quantities”

https://www.quora.com/What-are-thermodynamic-variables-and-state-variables

Bottom line: Properties like temperature, pressure, volume, internal energy, entropy, enthalpy, etc. can be described as state variables or simply thermodynamic variables because the difference in their values between any two equilibrium states does not depend on the process (path) connecting the states. The thermodynamic quantities of heat and work are not state variables because they depend on the path connecting the states.

Hope this helps.

• Thanks for answering , but i am asking about the difference between thermodynamic variable and state variable but your answer seems to tell about the difference between state variable and state function ( if i am not wrong)
– Xyz
Commented Dec 18, 2021 at 16:55
• I've updated my answer. Commented Dec 18, 2021 at 17:58
• Ok It helped...
– Xyz
Commented Dec 19, 2021 at 4:40
• The all encompassing term is “ thermodynamic property”. See en.m.wikipedia.org/wiki/List_of_thermodynamic_properties Commented Dec 19, 2021 at 6:24