# What is Equilibrium Vapor Pressure?

##### Joseph Hebert
Owner at - HVAC Buster

Joseph is an HVAC technician and a hobbyist blogger. He’s been working as an HVAC technician for almost 13 years, and he started blogging just...Read more

Equilibrium vapor pressure is the pressure exerted by a vapor in equilibrium with its non-vapor phases. The equilibrium vapor pressure is an indication of a liquid’s evaporation rate. It is also known as saturation vapor pressure or maximum vapor pressure.

The term “equilibrium” refers to the fact that the molecules of the substance are constantly moving between the gas and liquid phases, but there is no net change in either phase.

The equilibrium vapor pressure of a given substance is the pressure at which the gas and liquid phases are in equilibrium. The higher the vapor pressure, the more volatile the substance. The boiling point of a substance is directly related to its vapor pressure; the higher the vapor pressure, the lower the boiling point.

The Vapor Pressure of Water: Water has a very high vapor pressure. At room temperature (68°F or 20°C), water has a vapor pressure of 17.5 psi (1 atmosphere = 14.7 psi).

This means that if you have a glass of water sitting out, it will slowly start to evaporate until there is no water left in the glass. At 100°C, water’s equilibrium vapor pressure increases to over 400 psi! This is why we see steam coming off of hot water; there is so much evaporation occurring that some of it has to escape as gas form rather than remaining in liquid form.

## What is the Equilibrium Vapor Pressure of a Liquid

The equilibrium vapor pressure (EVP) of a liquid is the pressure at which the liquid and its vapor are in thermodynamic equilibrium with each other. The EVP is determined by the temperature of the liquid; it increases as the temperature increases. When a liquid is heated, its molecules gain kinetic energy and move faster.

Some of the molecules will have enough energy to overcome the intermolecular forces that hold them in the liquid state, and they will escape into the gas phase. As more molecules escape into the gas phase, the pressure of the gas increase. This increase in pressure exerted by the gas on the walls of its container is called vapor pressure.

At some point, there will be enough molecules in both phases (liquid and gas) so that there is no net movement between them; this state is called equilibrium. The vapor pressure at this point is called equilibrium vapor pressure (EVP). The EVP varies depending on what substance you are looking at; water has a much higher EVP than does gasoline, for example.

In general, as temperature increases, so does EVP; this makes intuitive sense because as things get hotter, particles move faster and have more kinetic energy to overcome intermolecular forces and escape into the gas phase. However, once a substance reaches its boiling point, further increases in temperature will not lead to further increases in EVP because all ofthe molecules now have enough kinetic energy to escape intogas formandthevaporpressurewill equal atmosphericpressure(at sea level).

## Which is True of Vapor Pressure

Vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases. The vapor pressure of a liquid is usually lower than the surrounding atmospheric pressure, unless the liquid is heated or the surrounding pressure is reduced. For example, water at room temperature has a much lower vapor pressure than does steam at the same temperature.

The value of vapor pressure increases as temperature increases for most materials. This relationship can be explained by considering the kinetic energy of molecules. At higher temperatures, molecules have more kinetic energy and are thus more likely to escape from the surface of a liquid into the gas phase.

The increased number of molecules in the gas phase results in an increase in vapor pressure.

## Vapor Pressure And Intermolecular Forces

Vapor pressure is the pressure of a gas in equilibrium with its non-vaporized phases. The vapor pressure of a liquid is the equilibrium pressure from a liquid or solid at a given temperature in which the molecules leaving the surface of the liquid equal those returning to it.*

Intermolecular forces (IMF) are attractive or repulsive forces between molecules. These forces determine many properties of matter, including boiling point, solubility, and melting point. The strength of IMFs increases as molecules get closer together.

London dispersion forces are the weakest type of intermolecular force and are present in all molecules. Hydrogen bonding is a stronger type of intermolecular force that occurs when there is a hydrogen atom bonded to a highly electronegative atom, such as nitrogen or oxygen.**

The relationship between vapor pressure and intermolecular forces can be explained using the kinetic molecular theory. This theory states that particles in a gas are constantly moving and colliding with each other and with the walls of their container. When two particles collide, they exert an equal and opposite force on each other.

The magnitude of this force is determined by the masses of the particles and by their velocities. The collisions between particles cause them to change direction; however, they do not change their speed unless they collide with something much more massive than themselves, such as the walls of their container.*

The average kinetic energy of the particles in a gas is proportional to its absolute temperature (in Kelvin). As temperature increases, so does average kinetic energy. Atoms or molecules traveling faster have more kinetic energy than those traveling slower.

When collisions occur between fast-moving and slow-moving particles, some energy is transferred from the fast-moving particle to the slow-moving one.* The velocity distribution curve for a sample of gaseous atoms or molecules at any given instant would look like a bell curve centered aroundthe mean velocity (vm), with most particles having velocities close to vm but fewer having either very high or very low velocities.* If we could measurethe speedsof all then molecule present inthe sampleat onceand plot themas afunctionof speedwe would get whatis calledavelocitydistributioncurve(Figure 1).

## What is the Equilibrium Vapor Pressure of a Liquid How is It Measured

The vapor pressure of a liquid is the pressure at which the liquid will change state into a gas. The equilibrium vapor pressure is the point where the two states are in balance with each other, and no further change will occur. This pressure is dependent on the temperature of the liquid, and can be measured using a variety of methods.

One common method is to use a manometer, which measures the difference in pressure between the gas and atmosphere. The atmospheric pressure pushes down on the liquid, while the vapor molecules push up against it. By measuring this difference, the vapor pressure can be determined.

Another method for measuring equilibrium vapor pressure is through freezing-point depression. This works by cooling a sample of the substance until it solidifies, then measuring how far below freezing it has become. The more volatile a substance is, the lower its freezing point will be.

By knowing how much lower than freezing point it becomes, we can calculate its equilibrium vapor pressure. Knowing the equilibrium vapor pressure of a substance can be useful in many applications. For instance, it can help us determine whether or not a given reaction will proceed to completion or not; if one reactant has a much higher vapor pressure than another then it will likely escape from the reaction before it has finished happening (this process is called “leakage”).

## What is a Equilibrium Vapor Pressure in Chemistry?

In chemistry, equilibrium vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases. The equilibrium vapor pressure is an indication of a liquid’s evaporation rate. It relates to the tendency of molecules and atoms to escape from a liquid or solid.

## What Determines Equilibrium Vapor Pressure?

In order to understand what determines equilibrium vapor pressure, it is first important to have a general understanding of what vapor pressure is. Vapor pressure is the pressure of a gas in equilibrium with its non-vapor (liquid or solid) phase. The higher the vapor pressure, the more likely it is for the liquid to evaporate into a gas.

There are several factors that can influence the vapor pressure of a liquid, but the two most important are temperature and intermolecular forces. Generally speaking, as temperature increases, so does vapor pressure. This makes sense when you think about it in terms of energy – at higher temperatures, molecules have more kinetic energy and are more likely to escape from the surface of a liquid into the gas phase.

The other major factor influencing vapor pressure is intermolecular forces. liquids with weaker intermolecular forces will have higher vapor pressures than those with stronger intermolecular forces. This again has to do with energy – it takes less energy for molecules to escape from a liquid if there are fewer attractive forces holding them in place.

So, to summarize, equilibrium vapor pressure is determined by both temperature and intermolecular forces. At higher temperatures or when intermolecular forces are weaker, vapors will be more likely to form and equilibrium vapor pressures will be higher.

## What is Dynamic Equilibrium And How Does It Relate to Vapor Pressure?

In a chemical reaction, dynamic equilibrium is the state in which the concentrations of the reactants and products remain constant over time. This occurs when the forward and reverse reactions are happening at the same rate. Vapor pressure is a measure of how much vapor is present in a given space.

It is affected by temperature, with higher temperatures leading to higher vapor pressures. When a liquid is in contact with its own vapor, they are in equilibrium. The vapor pressure of a liquid is equal to the partial pressure of the gas above the liquid.

## How Does Vapor Pressure Affect Equilibrium?

Most people are familiar with the concept of equilibrium. In a chemical reaction, equilibrium is the point at which the concentrations of the reactants and products remain constant. The forward and reverse reactions are occurring at equal rates, so there is no overall change in the concentrations of the substances involved.

Vapor pressure is a measure of the tendency of a substance to evaporate. When a substance vaporizes, it goes from the liquid state to the gas state. The higher the vapor pressure, the more likely it is that a substance will vaporize.

The relationship between vapor pressure and equilibrium can be illustrated by considering a container of water with some ice cubes in it. As long as there is ice present, the water will remain in its liquid state. This is because the partial pressure of water vapor in equilibrium with ice is lower than the saturated vapor pressure of water at room temperature.

Once all of the ice has melted, however,the partial pressures become equal and water starts to evaporate until an equilibrium concentration is reached once again. In general, when a reaction mixture contains more products than reactants (or vice versa),the side with more molecules will have a higher partial pressure. The higher partial pressure will cause more molecules to escape from that side into the surroundings until equilibrium is reached once again.

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## Conclusion

Equilibrium vapor pressure is the pressure exerted by a gas when it is in equilibrium with its liquid or solid phase. The equilibrium vapor pressure of a substance is the pressure at which the gas and liquid phases are in equilibrium. The higher the vapor pressure, the more volatile the substance.

Joseph is an HVAC technician and a hobbyist blogger. He’s been working as an HVAC technician for almost 13 years, and he started blogging just a couple of years ago. Joseph loves to talk about HVAC devices, their uses, maintenance, installation, fixing, and different problems people face with their HVAC devices. He created Hvacbuster to share his knowledge and decade of experiences with people who don’t have any prior knowledge about these devices.