# Total Pressure of 2-Phase System: Dalton's Partial Pressure Law

• losetowin
In summary, according to Dalton's partial pressure law, the sum of total partial pressures of each gas component in a 2 phase system is equal to the total pressure of the gas. However, it may be inaccurate to not account for the pressure of the liquid phase also, as described by Dalton's law which only applies to gases. The hydrostatic pressure caused by the liquid form may vary depending on the pressure being calculated, as discussed in a thread on physicsforums.com.
losetowin
Sum of Partial Pressures of Gas phase equals to total pressure of a 2 phase system? It sounds illogical because in a 2 phase system, the liquid phase also exerts pressure as well. Under dalton's partial pressure law, it states that the sum of total partial pressures of each gas component is equals to the total pressure of the gas.

y(i) Ptotal + y(j) Ptotal =Ptotal

If this law is applicable even to a 2 phase system, wouldn't it be inaccurate to not account for the pressure of the liquid phase also?

Dalton's law describes behavior of gases.

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So as to state, if I have a closed container at 1 atm that has 2 component 2 phases of liquid air, liquid water and gaseous air, gaseous water, the partial pressure of gaseous water is then y(H20) x Ptotal whereby Ptotal = 1 atm. Since we are using Ptotal in the calculations, would we ignore the hydrostatic pressure caused by the liquid form as well?

Hydrostatic pressure means that pressure on the bottom of the container differs from the pressure on the liquid surface. Whether you take it into account or not depends on what pressure you are calculating - it is not constant inside.

## 1. What is Dalton's Partial Pressure Law?

Dalton's Partial Pressure Law states that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of each individual gas in the mixture. This means that in a 2-phase system, the total pressure is the sum of the partial pressures of the liquid and gas phases.

## 2. How is the total pressure of a 2-phase system calculated using Dalton's Partial Pressure Law?

To calculate the total pressure of a 2-phase system using Dalton's Partial Pressure Law, you need to know the partial pressures of each individual gas in the mixture. Then, you simply add these partial pressures together to get the total pressure of the system.

## 3. What is the relationship between partial pressure and mole fraction in a 2-phase system?

The mole fraction of a gas in a 2-phase system is equal to the ratio of its partial pressure to the total pressure of the system. This means that the higher the mole fraction of a gas, the higher its partial pressure will be in the system.

## 4. How does temperature affect the total pressure of a 2-phase system?

According to Dalton's Partial Pressure Law, the total pressure of a 2-phase system is independent of temperature. This means that as long as the partial pressures of each gas remain constant, the total pressure of the system will not change with temperature.

## 5. Can Dalton's Partial Pressure Law be applied to non-ideal gases?

Yes, Dalton's Partial Pressure Law can be applied to both ideal and non-ideal gases. However, for non-ideal gases, corrections must be made to account for deviations from ideal behavior. These corrections can be made using equations such as the van der Waals equation or the Redlich-Kwong equation.

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