# Vapor-Liquid Equilibrium Calculations

• runningman19
In summary, the problem is a mass balance problem where the total number of moles in the liquid and vapor is 10. At a temperature of 88 C, there is 40 mol% methanol in the gas phase and 10 mol% in the liquid phase. Using this information and solving for the number of moles in the liquid phase, it is determined that 1/3 mole of methanol remains in the liquid.
runningman19
Hi Everyone,
I am having trouble grasping the concept of Raoult's law, partial pressures etc. One problem in specific is: A system contains 3 moles of methanol and 7 moles of water at 25 degrees celsius. The temperature is raised until there is 40 mol% methanol in the gas phase. How much is left in the liquid phase?
The Txy diagram is attached.
Thanks so much guys,
Nick

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• Txy.png
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This is strictly a mass balance problem. Let L represent the total number of moles in the liquid and W represent the number of moles in the vapor. So, $$L+V = 10$$

From the diagram, there is 40 mol% methanol in the gas phase ( y = 0.4) when the temperature is 88 C. And the mole percent in the liquid at this state is 10 % (x = 0.1). So, the mass balance on the methanol is $$L(0.1)+V(0.4)=3$$So, solving these equations simultaneously for L and V, we obtain:$$L=\frac{10}{3}$$and $$V=\frac{20}{3}$$So the amount of methanol remaining in the liquid is ##\frac{10}{3}(0.1)=\frac{1}{3}\ mole##.

## 1. What is Vapor-Liquid Equilibrium (VLE) and why is it important in scientific research?

Vapor-Liquid Equilibrium (VLE) is the state of a system at which the liquid and vapor phases are in equilibrium with each other. It is important in scientific research because it helps us understand the behavior and properties of mixtures, which are commonly found in many chemical and industrial processes.

## 2. How is VLE calculated?

VLE can be calculated using thermodynamic models such as the Raoult's Law, Antoine's Equation, or the Van Laar Equation. These models use experimental data such as temperature, pressure, and composition to determine the equilibrium between the liquid and vapor phases of a mixture.

## 3. What factors affect VLE calculations?

The factors that affect VLE calculations include temperature, pressure, composition of the mixture, and the type of thermodynamic model used. Other factors such as intermolecular forces, molecular size, and polarity can also play a role in VLE behavior.

## 4. What are the applications of VLE calculations?

VLE calculations have various applications in industries such as chemical, pharmaceutical, and food production. They are used to design and optimize processes, determine the feasibility of a reaction, and predict the behavior of mixtures under different conditions.

## 5. How accurate are VLE calculations?

The accuracy of VLE calculations depends on the thermodynamic model used and the quality of the experimental data. Some models may be more accurate for certain mixtures, while others may not be suitable. It is important to validate VLE calculations with experimental data to ensure their accuracy.

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