# What is Water 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

Water vapor pressure is the pressure of water vapor in the air. It is affected by temperature, humidity, and atmospheric pressure. At higher temperatures, more water vapor can be present in the air.

At lower temperatures, less water vapor can be present in the air. The amount of water vapor in the air also affects the amount of pressure that it exerts.

Water vapor pressure is the pressure of water vapor in the air. It is affected by temperature, humidity, and atmospheric pressure. At high temperatures, water vapor pressure increases.

At low temperatures, it decreases. The higher the humidity, the higher the water vapor pressure. The lower the atmospheric pressure, the lower the water vapor pressure.

## Water Vapor Pressure at 25 C

Water vapor pressure is the pressure of water vapor in the air. It is affected by temperature, humidity, and atmospheric pressure. At 25 degrees Celsius, water vapor pressure is 17.54 kPa.

## Vapor Pressure of Water at 20 C

Vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases. The vapor pressure of water is the pressure at which water vapor is in equilibrium with its liquid phase. The value for the vapor pressure of water at 20 °C (68 °F) is 3.17 kPa.

The saturated vapor pressure curve for water intersects the horizontal line corresponding to the triple point at 611.73 Pa and 273.16 K (−38.87 °C). This shows that, at temperatures below the triple point, a mixture of ice and water can coexist in equilibrium, with both phases present simultaneously; when this happens, the partial pressures of each component add up to create the total Vapor Pressure Of Water At 20 C .

## Vapor Pressure of Water in Mmhg

Vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases. The term can be used for liquids, solids, and gases. Vapor pressure is commonly measured in mmHg (millimeters of mercury).

For water at standard temperature and pressure (STP), the vapor pressure is 0.0061 mmHg. The vapor pressure of a given substance varies with temperature; as the temperature increases, so does the vapor pressure. The relationship between vapor pressure and temperature can be described by the Clausius–Clapeyron equation:

\ln P_{\text{vap}} = \frac{\Delta H}{R} \left( \frac{1}{T_2} – \frac{1}{T_1}\right) + \ln P_0 where P vap is the vaporpressure of the substance at temperature T 2 , ΔH is the heat of vaporization, R is the universal gas constant, T 1 is a reference temperature, and P 0 is a reference vaporpressure. For water, ΔH = 40.6 kJ/mol and R = 8.314 J/mol·K.

Thus, we can plug these values into the Clausius–Clapeyron equation to find that: ln(P_{vap}) = \frac{40600}{8.314} \left(\frac{1}{298} – \frac{1}{T}\right) + ln(0.0061) or

ln(P_{vap}) = 9990 T^{-1} – 16290 + ln(0.0061) which can be simplified to: P_{vap} = e^{-(16290/T)}e^{-(9990/T)}0.0061mmHg

From this equation we see that as T goes to infinity, P vap also goes to infinity – meaning that there is no maximum possible vaporpressure for water (or any other substance). However, as T approaches 0 K (-273°C),P vap approaches zero – meaning that there is a minimum possible vaporpressure for water (and any other substance).

## Pressure of Water

When it comes to the pressure of water, there are a few things that you need to know. For starters, water is a molecule made up of two hydrogen atoms and one oxygen atom. These molecules are constantly moving and bouncing around.

When they hit something, they exert a force on that object. The more molecules there are in a given area, the greater the pressure will be. Water pressure is measured in pounds per square inch (PSI).

The average pressure at sea level is 14.7 PSI. This means that for every square inch of your body that is exposed to the air, 14.7 pounds of water are pushing against it. The reason we don’t feel this constant pressure is because our bodies have evolved to equalize the pressures inside and outside.

The pressure of water can have both positive and negative effects on our lives. On the plus side, it helps us stay hydrated by keeping fluid in our cells and blood vessels. It also helps circulate blood throughout our bodies and eliminates waste products through urine and sweat.

On the downside, high blood pressure can lead to health problems like heart disease and stroke.

## Water Vapor Pressure Calculator

As the air temperature increases, so does the water vapor pressure. The saturated vapor pressure is the maximum amount of water vapor that can be in the air at a specific temperature. The calculator below can be used to estimate both the saturated and actual vapor pressures for various temperatures.

To use the calculator, enter the dry bulb temperature (T) and press ‘Calculate’. If you know both the wet bulb and dry bulb temperatures, you can also enter those values and press ‘Calculate’ to determine just the humidity ratio. Wet Bulb Temperature:

The wet-bulb temperature is the lowest temperature that can be reached by evaporating water into air at a constant atmospheric pressure with only latent heat transfers. In other words, it is how much heat is required to change liquid water into gas while taking into account any changes in energy due to latent heat of condensation or vaporization (sensible heat). The formula for calculating wet-bulb temperature makes use of Wet Bulb Globe Temperature (WBGT), which is a measure of heat stress in direct sunlight which takes into account: dry-bulb temperature, humidity, wind speed, and sun angle.

Dry Bulb Temperature: The dry-bulb temperature is simply a measure of air temperature taken with an ordinary thermometer. It indicates what one feels as warmth or coldness when holding their hand out in front of them or feeling their cheek; basically, how “hot” or “cold” it feels.

## What is Meant by the Vapor Pressure of Water?

When water is heated, the molecules gain kinetic energy and begin to move faster. Eventually, they will have enough energy to overcome the attractions holding them in the liquid state and will enter the gas state. The temperature at which this occurs is called the boiling point.

The vapor pressure of a liquid is a measure of how much pressure is required to prevent the liquid from boiling. The higher the vapor pressure, the more difficult it is to keep the liquid from boiling. Vapor pressure is affected by temperature; as temperature increases, so does vapor pressure.

Water has a very high vapor pressure; at room temperature (70°F or 21°C), its vapor pressure is 22.1 inches of mercury (inHg). This means that if you took a container of water and sealed it tightly, eventually enough water would evaporate into the air above it to create a Pressure inside the container that was equal to 22.1 inches of mercury. At this point, any further increase in temperature would cause the water to boil.

## What is Vapor Pressure Simple Definition?

Vapor pressure or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its non-vapor phases. All liquids and solids have a tendency to evaporate into a gaseous form, and all gases have a tendency to condense back into their liquid or solid state. The balance between these two processes is what determines the vapor pressure for each substance.

The higher the vapor pressure of a substance, the more likely it is to evaporate into a gas. For example, water has a relatively high vapor pressure (22.7 kPa at 20°C), which means that it readily turns into steam or water vapor when heated. On the other hand, substances like mercury metal have very low vapor pressures (0.0002 kPa at 20°C), meaning that they almost never turn into vapors under normal conditions.

There are several factors that affect vapor pressure, including temperature and intermolecular forces. In general, raising the temperature of a liquid will increase its vapor pressure; this is because more thermal energy is available to overcome the attractive forces between molecules, causing them to break apart and enter the gas phase.

## What is the Normal Vapor Pressure of Water?

The vapor pressure of water is the pressure at which water vapor exists in equilibrium with its non-vapor phases. The saturation vapor pressure is the vapor pressure of water at a given temperature. The normal boiling point of water is the temperature at which the saturated vapor pressure equals atmospheric pressure.

The following relationship holds true for all liquids: P = X*P° where P is the absolute vapour pressure, P° is the vapourpressure of the pure liquid at a given temperature, and X is the mole fraction of the gas phase. For water, this gives: P = Xw*Pw° where w denotes “water” and W indicates “vapour”. At 25 °C, the saturation vapour pressures are 3133 Pa for ice and 6113 Pa for steam (1 atmosphere = 101325 Pa).

So, if we take one mole of ice and one mole of steam at 25 °C and 1 atmosphere total pressure, then we have: 3133 Pa = (Xice)*(3133 Pa) + (Xsteam)*(6113 Pa) This implies that Xsteam must be 0.339 or 33.9%. That means that only about a third of our initial two moles are in gaseous form; most has condensed back into liquid water on account of the cooler temperature.

## Where is the Vapor Pressure of Water?

Water vapor pressure is the pressure of water vapor in the air. It is affected by temperature, humidity, and atmospheric pressure. The higher the temperature, the higher the water vapor pressure.

The higher the humidity, the lower the water vapor pressure. The higher the atmospheric pressure, the lower the water vapor pressure.

## Conclusion

Water vapor pressure is the pressure exerted by water vapor in the atmosphere. The higher the temperature, the higher the water vapor pressure. The amount of water vapor in the air also affects water vapor pressure.

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.