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Vapor Pressure Lowering Study Guide

On adding a non-volatile solute to a solvent, the vapor pressure of the solution lowers.

Introduction:

Even if you don't wish to study Julius Caesar's manuscripts, Latin is a fascinating and valuable language. Consider the word "colligative." What was the source of that? If you understand a little Latin, you'll realize that it's derived from two Latin words that mean "to connect." This will help you comprehend some of the scientific jargon we use daily.

In chemistry, a colligative attribute of a solution is determined only by the quantity of solute particles dispersed in the solution rather than their identity. The reduction of vapor pressure is one such colligative feature.

Reduction of Vapor pressure Source

VAPOUR PRESSURE:

The pressure exerted by vapors over a solution under equilibrium circumstances at a certain temperature is known as vapor pressure.

Vapour-Pressure Source

LOWERING OF VAPOUR PRESSURE:

Take a pure liquid as an example; the liquid particles occupy the liquid's surface. Assume that this homogeneous liquid now contains a non-volatile solute (substance that does not evaporate into gas under existing conditions). The vapor just above the solution is entirely of solvent molecules because the solute molecules are non-volatile. The vapor pressure of the mixture is observed to be decreased than that of the pure liquid at a specific temperature after the solute is added.

Because the solute was introduced to the pure liquid (solvent), the fluid surface now included particles of both the pure liquid and the solute, the vapor pressure dropped. The proportion of solvent molecules that escape into the vapor phase decreases, lowering the pressure produced by the vapor phase. This is referred to as relative vapor pressure reduction.

This drop-in vapor pressure is a colligative property (properties of solutions that depend on the ratio of the number of solute particles to the number of solvent particles in a solution). It is dependent on the amount of non-volatile solute added to the solution, regardless of its composition.

REAL-LIFE EXAMPLE OF VAPOR PRESSURE LOWERING:

1. LPG CYLINDERS:

An LPG cylinder can't feed fuel to a burner if it doesn't have enough vapor pressure. The valve will open when the burner knob is cranked and the vapor pressure rises. This permits the fuel's vapors to stream in the burner's direction.

LPG Cylinders Source

2. PRESSURE COOKER:

The principle of vapor pressure underpins the entire functioning of a pressure cooker. Water vapors develop when heat is applied to the ingredients put into the pressure cooker. The vapor pressure in the cookware tends to rise due to this. Pressure Cooker Source

3. HUMIDITY:

The relative humidity perceived by a person in a given place is one of the finest instances of vapor pressure in everyday life.

Humidity Source

CONCLUSION:

  • The pressure exerted by vapors over a solution under equilibrium circumstances at a certain temperature is known as vapor pressure.
  • On adding a non-volatile solute to a solvent, the vapor pressure of the solution becomes less compared to the vapor pressure of the pure solute. This lowers the vapor pressure of the solvent.

FAQs:

1. What is an application of vapor pressure lowering in real life?

An LPG cylinder can't feed fuel to a burner if it doesn't have enough vapor pressure.

2. Is a pressure cooker an example of vapor pressure lowering?

No, a pressure cooker is an example of high vapor pressure. But if you add salt to whatever you care about cooking, then yes, it will be an example of vapor pressure lowering.

3. Which substance has a lower vapor pressure?

Diethyl ether has lower vapor pressure.

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SOURCES:

  1. Vapor Pressure Lowering. https://www.ck12.org/c/chemistry/vapor-pressure-lowering/rwa/Putting-on-the-Pressure/ accessed 17 Feb 2022
  2. Vapor Pressure Lowering. https://courses.lumenlearning.com/cheminter/chapter/vapor-pressure-lowering/ accessed 17 Feb 2022
  3. Colligative Properties: Relative Lowering Of Vapour Pressure. https://byjus.com/chemistry/colligative-properties-relative-lowering-of-vapour-pressure/ accessed 17 Feb 2022