Vapour Liquid Equilibrium for a two component mixture.

[dharavsolanki]

I am studying vapor liquid eqilibrium for two component systems. There are some things which confuse me right now.

These are the questions: -

(1) Since there has to be atleast one phase, the degrees of freedom are maximum three. Which means, the degrees of freedom are P, T and composition. Why does composition automatically qualify as the third choice of variable?
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(2) We are plotting a surface in space P-T-Composition. So when we plot the srface what do we exactly draw/plot? The possible states the system an take? Or is it a forth property?<P>
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(3)The under surface and upper surface are saturated vapour and saturated liquid states. What are saturated states in this context?

 

[Almsco]

Hi there! It sounds like you are having some confusion with vapor liquid equilibrium. Let me try to answer your questions:

(1) The composition of the system automatically qualifies as the third choice of variable because it is related to the number of components in the system. In a two component system, there are two variables that can be used to describe the composition (e.g. the molar fraction of each component). These two variables are combined into one composition variable, which is then used as the third choice of variable.

(2) When you plot the surface in space P-T-Composition, you are plotting the possible states that the system can take. This means that you are plotting the possible values of temperature, pressure, and composition that the system can occupy.

(3) Saturated states in this context refer to states where the vapor and liquid phases of the system are in equilibrium. This means that the partial pressures of the components in the vapor and liquid phases are equal.

 

[charng]

Hello,

Vapor-liquid equilibrium for a two-component mixture is a complex but important concept in thermodynamics and chemical engineering. I understand that you have some questions about this topic, so I would like to offer some explanations and clarifications.

Firstly, the degrees of freedom in a system refer to the number of independent variables that can be varied to describe the state of the system. In the case of a two-component mixture, the three degrees of freedom are pressure (P), temperature (T), and composition. This is because the composition of the mixture is not fixed and can be adjusted by changing the amounts of the two components. Therefore, it is considered as an independent variable in this context.

Secondly, when we plot the surface in P-T-Composition space, we are essentially mapping out the possible states that the system can take at different combinations of pressure, temperature, and composition. This surface is known as the vapor-liquid equilibrium (VLE) surface and it represents the equilibrium conditions between the vapor and liquid phases. It is not a fourth property, but rather a graphical representation of the equilibrium states of the system.

Lastly, the saturated states in this context refer to the conditions at which the vapor and liquid phases coexist in equilibrium. This means that the system is at a point where the vapor and liquid phases have the same composition and are in equilibrium with each other. The under surface represents the saturated liquid state, while the upper surface represents the saturated vapor state.

I hope this helps to clarify your questions about vapor-liquid equilibrium for a two-component mixture. If you have any further questions or concerns, please do not hesitate to ask. it is important to continuously seek understanding and clarification in our studies. Keep up the good work in your research!