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Vapour Pressure Definition

The pressure that results from a liquid (or solid) condensing on its surface is referred to as vapour pressure. This pressure is made in a confined receptacle at a specific temperature during a thermodynamic equilibrium condition. The vapour pressure shows how quickly a liquid is vaporizing. The liquid meets its boiling point when the vapour and gas pressure are equal. In this writing, we will discover the characteristics of liquid vapour pressure.

Vapour Pressure Definition

Vapour Pressure

The propensity of a substance to transform into a vapour condition is known as vapour pressure. Also, the pressure that a liquid's vapour exerts on its condensed stages in a confined system is known as vapour pressure. Any liquid's air pressure rises in direct proportion to its temperature.

Several methods can determine a liquid's vapour pressure. Placing a manometer inside a flask or other confined receptacle is the easiest way to measure vapour pressure.

In all substances, there is a tendency towards evaporation. At the liquid's surface, the vaporization process takes place. In the liquid state, molecules from the liquid's surface can flee into space if their kinetic energy exceeds the pull force between molecules. The action is referred to as "evaporation."

If evaporation occurs in a confined container system, liquid vapours remain in touch with the liquid's surface. The condensing of molecules also carries out a constant random motion, like gas molecules. As a result of the collisions between the molecules during these motions, including those with the container walls, they lose energy and transform back into liquids. The procedure is referred to as condensation.

Condensation and Evaporation

Condensation and evaporation are ongoing processes. Consequently, evaporation and condensation reach a state of balance at a fixed temperature after some time. The condition is steady at a fixed temperature when the quantity of molecules in the vapour comes to equilibrium. The intermolecular force of pull increases with temperature, which affects the liquid's vapour pressure. When the temperature rises, the vapour pressure of a liquid grows and diminishes.

However, as time goes on, the condensation rate and molecules present in the liquid phase increase. When that happens, the rate of condensation and vaporization are identical. The pressure exerted by molecules in this situation, as shown by the manometer, is called the liquid's vapour pressure. The pressure the liquid's surrounding vapours exerts is known as vapour pressure.

Vapour Pressure Characteristics

Vapour pressure is solely influenced by temperature. No matter how much liquid is in the container, one liter or 40 liters of liquid will have the same vapour pressure at the same temperature. Temperature and vapour pressure have an exponential relationship, which indicates that as temperature increases, so does vapour pressure.

A pure liquid experiences more vapour pressure than a liquid in solution.

Vapour Pressure Influencing Factors

Vapour pressure relies on several variables which are as follows:

1. Liquid's Nature

The liquid's intermolecular forces are used to describe its structure. The gaseous pressure will decrease as the strength of the intermolecular interactions increases, in other words.

2. Solute Concentration

A substance in the liquid will greatly lower the vapour pressure. The decline in vapour pressure also varies depending on the solute content.

3. Temperature Effect

The liquid's kinetic energy increases as its temperature rises, and because of this increase in rotational energy, molecules are more likely to escape, which increases vapour pressure. As a result, we can determine that temperature and air pressure are proportionate.

4. Humidity has No Effect on Vapour Pressure

Temperature is the only factor influencing the vapour pressure for a specific quantity of air-water vapour. Only when every other element is consistent will humidity have an effect. Therefore, avoid mixing up the impact of temperatures and humidity.

5. Volume

The capacity of the receptacle typically has little impact on vapour pressure. As we already know, the area's liquid and vapour will be in balance. Consider that the volume of the surface is divided into infinite component volumes, changing its volume and declaring it decreased.

As a result, some of the container's vapour will also transform into a liquid form, and some of the liquid will inevitably turn into its vapour form as the amount increases.

6. Area of Surface

Typically, surface size has no impact on vapour pressure.

Factors affecting Liquid Vapour Pressure

However, the following elements impact a liquid's stable vapour pressure:

1. Forces of Intermolecular Attraction

Intermolecular forces are any forces, such as powers of attraction or repulsion, that facilitate a relationship between atoms. For instance, the covalent connection, which involves exchanging electron pairs between atoms, is much more powerful than the intermolecular force between nearby molecules.

2. The Liquid's Present Volume

The amount of the liquid does not influence the equilibrium vapour pressure of the liquid. While maintaining a steady temperature, a liquid's volume can be shifted, but its equilibrium vapour pressure won't move.

3. The Liquid's Temperature

When a fluid is in equilibrium, its vapour pressure rises as its temperature rises or the intermolecular forces of attraction diminish.

FAQs on the Vapour Pressure

1. What are liquid's properties?


Liquid's properties are:

  1. Liquids typically don't have rigid properties. They don't have a distinct shape, but they do have a distinct volume.
  2. Intermolecular forces, space, and kinetic energy are all moderately strong. A liquid is anything like water.
  3. In comparison to solids and gases, liquids are more compressible by nature.

2. Difference between vapour pressure and boiling point


Parameter Vapour Pressure Boiling Point
1. Definition It is the pressure that a liquid or solid substance releases as vapour in a closed container or space. It is the temperature where the liquid's vapour pressure is the same as the pressure being applied to it from outside.
2. Specific Conditions It is determined for the enclosed system with a uniform temperature. It is determined for the system which has constant pressure.
3. Physical States It varies based on the temperature. It varies based on the atmospheric pressure.
4. Variations It is related to liquid and solid phases. It is related to the liquid phase.

3. What is the vapour pressure unit?


The most utilized unit for it is torr.

4. Which has the highest vapour pressure?


The substance with a low boiling point will have a highvapour pressure at normal temperature.

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