Vapour Pressure and External Pressure

In summary, when a liquid is placed in a vacuum, it will not necessarily boil unless it exists as a gas in that vacuum. The vapor pressure of a substance in a vacuum is dependent on its temperature, and if the vapor pressure is positive, the substance will evaporate. However, the details of the environment and the substance itself will also play a role in determining if and how it will evaporate in a vacuum.
  • #1
Harmony
203
0
When the vapour pressure of a liquid equals to the external pressure, the liquid will boil.
So, what if a liquid is placed in a vacum? Will the liquid boil instantly when heated?
 
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  • #2
It depends on the liquid and the temperature, but many will boil at room temperature in a vacuum.
 
  • #3
Temperature is a measure of the average kinetic energy of molecules.

A Vacuum is devoid of all matter by definition and therefore has no temperature.

If your substance exists as a liquid state in a vacuum, then it will not boil; however, if it exists as a gas in vaccum, then it will boil. (Actually, boiling occurs because of microscopic bumps on the pot that agitate the liquid. It would probably turn to vapor directly without boiling in outer-space)

You won't have to add heat to achive this, it will occur spontaneously.
 
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  • #4
How do we know whether a substance will exist in liquid or gas form in vaccum?
 
  • #5
Vapor pressure of a liquid (or even a solid) is a function of temperature.
For sure, if it is positive the substance will evaporate when placed in vacuum.
This doesn't mean that this will happen like in a boiling pan.
The details will play a role: is it in microgravity of not, is the temperature uniform or is there a temperature gradient, is the substance in contact with some other material, ...
 

1. What is vapour pressure?

Vapour pressure is the pressure exerted by the gaseous form of a substance in equilibrium with its liquid or solid form at a given temperature. It is a measure of the tendency of a substance to escape or evaporate into the surrounding atmosphere.

2. How is vapour pressure affected by external pressure?

Vapour pressure is directly proportional to external pressure. As external pressure increases, the vapour pressure also increases. This is because an increase in external pressure leads to a decrease in the volume of the gas, making it more difficult for the particles to escape into the gas phase.

3. What factors affect vapour pressure?

The main factors that affect vapour pressure are temperature, intermolecular forces, and surface area. As temperature increases, so does vapour pressure. Stronger intermolecular forces and a larger surface area also lead to higher vapour pressure.

4. How does vapour pressure relate to boiling point?

Vapour pressure and boiling point are inversely related. As vapour pressure increases, the boiling point decreases. This is because at higher vapour pressure, the substance can transition from liquid to gas phase more easily, resulting in a lower boiling point.

5. Why is vapour pressure important in everyday life?

Vapour pressure plays a crucial role in a variety of everyday processes, such as cooking, evaporation, and distillation. It also affects the weather, as changes in vapour pressure can lead to the formation of clouds and precipitation. Additionally, vapour pressure is used in many industrial processes, including refrigeration and chemical reactions.

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