Partial Pressure Question

In summary: Assuming that they are both superheated vapors in the gas phase, what is the saturation temperature (dew point) for each of these...assuming they are in equilibrium?The saturation temperature for water is 100°C. The saturation temperature for the imaginary substance is also 100°C. Excellent. Now you have a cylinder that has equal molar amounts of water and immiscible substance at 1 atm, such that the partial pressure of each is 0.5 atm. The temperature is 99C.
  • #1
RoshDawg
6
0
Hello, first post here.
Here is a hypothetical partial pressure of gas question

Imagine you have a two component system:
Component 1 is water
Component 2 is an imaginary substance that is immiscible with water, but has same boiling temp / pressure

You put the two components in a pressurized cylinder with equal molar volume distribution, and set the pressure to 1atm and 99°C (of course we know pure water will be liquid at this stage). Partial pressure law implies that water (or steam) will be exerting .5 atm, as would component 2 (.5 atm and 99°C will yield a vapor). Will there be liquid water or steam inside the cylinder?

Thanks for the help!
 
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  • #2
RoshDawg said:
Hello, first post here.
Here is a hypothetical partial pressure of gas question

Imagine you have a two component system:
Component 1 is water
Component 2 is an imaginary substance that is immiscible with water, but has same boiling temp / pressure

You put the two components in a pressurized cylinder with equal molar volume distribution, and set the pressure to 1atm and 99°C (of course we know pure water will be liquid at this stage). Partial pressure law implies that water (or steam) will be exerting .5 atm, as would component 2 (.5 atm and 99°C will yield a vapor). Will there be liquid water or steam inside the cylinder?

Thanks for the help!
Suppose you had pure liquid water in a container (with no imaginary immiscible substance present), and you held the pressure at 0.5 atm (absolute) while raising the temperature to 99 C. What would the state of the contents of the container?

Chet
 
  • #3
Chestermiller said:
Suppose you had pure liquid water in a container (with no imaginary immiscible substance present), and you held the pressure at 0.5 atm (absolute) while raising the temperature to 99 C. What would the state of the contents of the container?

Chet

You would be in a vapor phase
 
  • #4
RoshDawg said:
You would be in a vapor phase
To be more precise, you would have superheated steam at 0.5 atm and 99 C. There would be no liquid water present. Now you do the same problem for the pure immiscible substance at 0.5 atm absolute and 99 C. What would be the state of the immiscible substance?
 
  • #5
Chestermiller said:
To be more precise, you would have superheated steam at 0.5 atm and 99 C. There would be no liquid water present. Now you do the same problem for the pure immiscible substance at 0.5 atm absolute and 99 C. What would be the state of the immiscible substance?

Oh yes you are correct. Imagine the immiscible substance has the same thermodynamic properties. I am just wondering if water should be treated as if it is under 1atm conditions or .5atm due to partial pressure. Meaning if the water in the 1atm cylinder would have vaporized or remained as a liquid, when there is another substance in the cylinder taking up have the volume and exerting half the pressure.

Sorry if I am explaining the question poorly. I am vaporizing hydrocarbons and water and am wondering if I should take into account partial pressures or not.
 
  • #6
RoshDawg said:
Oh yes you are correct. Imagine the immiscible substance has the same thermodynamic properties. I am just wondering if water should be treated as if it is under 1atm conditions or .5atm due to partial pressure. Meaning if the water in the 1atm cylinder would have vaporized or remained as a liquid, when there is another substance in the cylinder taking up have the volume and exerting half the pressure.

Sorry if I am explaining the question poorly. I am vaporizing hydrocarbons and water and am wondering if I should take into account partial pressures or not.
Yes. I understand what you are trying to figure out. I'm just trying to help you figure it out by leading you to the solution gradually. So, please answer my question in my previous post about the pure immiscible substance.

Chet
 
  • #7
Chestermiller said:
Yes. I understand what you are trying to figure out. I'm just trying to help you figure it out by leading you to the solution gradually. So, please answer my question in my previous post about the pure immiscible substance.

Chet

The pure immiscible substance has the same thermodynamic properties as the water. So at .5atm and 99°C, it is a gas. At 1atm and 99°C, it is liquid.
 
  • #8
RoshDawg said:
The pure immiscible substance has the same thermodynamic properties as the water. So at .5atm and 99°C, it is a gas. At 1atm and 99°C, it is liquid.
Excellent. Now you have a cylinder that has equal molar amounts of water and immiscible substance at 1 atm, such that the partial pressure of each is 0.5 atm. The temperature is 99C.

Assuming that they are both superheated vapors in the gas phase, what is the saturation temperature (dew point) for each of these substances corresponding to a saturation vapor pressure is 0.5 atm?

Chet
 
  • #9
Chestermiller said:
Excellent. Now you have a cylinder that has equal molar amounts of water and immiscible substance at 1 atm, such that the partial pressure of each is 0.5 atm. The temperature is 99C.

Assuming that they are both superheated vapors in the gas phase, what is the saturation temperature (dew point) for each of these substances corresponding to a saturation vapor pressure is 0.5 atm?

Chet

The saturation temperature would be 82°C at .5atm for both substances
 
  • #10
RoshDawg said:
The saturation temperature would be 82°C at .5atm for both substances
So, if nothing would condense out, you have your answer to your original question.
 
  • #11
Okay, so just to recap, both fluids will be in gas phase since both should be in gas phase at .5 atm at 99C, even though the cylinder is set to 1atm, due to partial pressure of .5atm for each substance. Is this correct?
Thanks for your help in this.
 
  • #12
RoshDawg said:
Okay, so just to recap, both fluids will be in gas phase since both should be in gas phase at .5 atm at 99C, even though the cylinder is set to 1atm, due to partial pressure of .5atm for each substance. Is this correct?
Thanks for your help in this.

Yes. You pretty much doped this out for yourself.

Chet
 
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1. What is partial pressure?

Partial pressure is the pressure exerted by a single gas in a mixture of gases. It is proportional to the concentration of that gas and the total pressure of the mixture.

2. How is partial pressure calculated?

Partial pressure can be calculated by multiplying the total pressure of the mixture by the mole fraction of the gas in question. The mole fraction is the ratio of the number of moles of the gas to the total number of moles in the mixture.

3. Why is partial pressure important in gas laws?

Partial pressure is important in gas laws because it allows us to analyze the behavior of individual gases in a mixture. This is particularly useful in situations where different gases have different properties, such as in atmospheric gases or in gas mixtures used in industrial processes.

4. How does temperature affect partial pressure?

According to the ideal gas law, pressure is directly proportional to temperature. Therefore, as temperature increases, the partial pressure of a gas will also increase. This is because the molecules of the gas have more kinetic energy and collide with the container walls more frequently, increasing the pressure.

5. What is the relationship between partial pressure and gas solubility?

The partial pressure of a gas above a liquid is directly proportional to its solubility in that liquid. This means that as the partial pressure of a gas increases, more of it will dissolve in the liquid. This relationship is described by Henry's law.

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