thermodynamics coordinate

renhoran

i don't really understand which quantities are thermodinamic coordinates and which are not. and what makes work and heat are not thermodinamic coordinates but temperature, volume, etc are thermodinamic coordinates?

rock.freak667

What do you mean by "thermodynamic coordinates"? If you mean those P-V, T-S, P-H diagrams and such then work and heat are as a result of the changes in pressure, temperature, enthalpy and so on.

So it makes more sense to plot state changes rather than the work done in the process.

Philip Wood

Take the simple example of a sample of gas with a fixed number of molecules. It need not be ideal. Its temperature, T, can be expressed as a function of just two variables, volume, V, and pressure, p. We can, it turns out, express all gas properties as functions of just two variables (such as p and V or p and T). These properties include refractive index, viscosity, internal energy, entropy, enthalpy, the Helmholtz function, the Gibbs function. We call these properties 'functions of state'. The state is determined by the values of just two variables.

Heat and work are not functions of state. They are not properties of the gas. They both represent energy in transit to or from the system, not energy residing in the system.