Thermodynamics: Single/Homogeneous Phase Differences

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Discussion Overview

The discussion centers on the distinctions between single phase and homogeneous phase in thermodynamics, particularly in relation to fundamental thermodynamic relations and their applicability to systems of varying compositions. Participants explore the implications of these terms in both single-component and multi-component systems, as well as during phase changes.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that a single phase refers to a material being entirely in one state (solid, liquid, or gas), while a homogeneous phase indicates spatial uniformity.
  • There is a discussion on the applicability of the relation dg = vdp - sdT to single-component systems versus multi-component systems, with some arguing that constant composition implies unchanging mole fractions.
  • Participants question whether a liquid-vapor water system can be considered a homogeneous phase with constant composition, noting that it consists of two phases that are each homogeneous.
  • Some participants explore how to apply the Gibbs free energy equation during phase changes, suggesting that the equation may not apply to the entire system due to the presence of different phases.
  • There is a mathematical exploration of how Gibbs free energy changes during phase transitions, with references to the Clapeyron Equation and the conditions under which it holds.
  • Participants express confusion regarding the application of thermodynamic equations in systems where mass transfer occurs and how this affects the definitions of homogeneous phase and constant composition.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the definitions and implications of single phase versus homogeneous phase, particularly in the context of multi-component systems and phase changes. Multiple competing views remain regarding the applicability of thermodynamic relations in these scenarios.

Contextual Notes

Some limitations are noted regarding the assumptions made about constant composition and the definitions of phases during equilibrium and phase changes. The discussion highlights the complexity of applying thermodynamic principles to systems with varying compositions and phases.

  • #31
I tried , but cannot think of any experimental way . I guess my domain of knowledge is restricted to theoretical part .
 
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  • #32
Rahulx084 said:
I tried , but cannot think of any experimental way . I guess my domain of knowledge is restricted to theoretical part .
What you would do is prepare 2 samples of the gas with n moles total in each. The number of moles of species i in each sample would then be ##n_{i}=nx_{i}##. In one of these samples you would then add a small amount of species i so ##n_{i}=nx_{i}+\delta##. You would then compress each of these samples at temperature T from low pressure to pressure P, and measure ##nZ_{i}=\frac{PV}{RT}## at each intermediate pressure along the way. Then, from the two samples at each pressure along the way, you would evaluate ##\bar{Z_i}=\frac{\Delta nZ_{i}}{\delta}## between the two samples. Then you would use these values to evaluate the integral.
 
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