Calculate water vapor pressure from temperature, or find temperature from vapor pressure, using the Antoine equation in °C, °F, K, kPa, atm, mmHg, or psi.
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Water Vapor Formula
The following (Buck) equation is commonly used to approximate the saturation water vapor pressure.
P = 0.61121 × e((18.678 – T/234.5) × (T/(257.14 + T)))
- Where P is the saturation vapor pressure (kPa)
- T is the temperature (°C)
Water Vapor Pressure Definition
Water vapor pressure is the force exerted by water vapor molecules in the air.
It represents the partial pressure of water vapor in a mixture of gases. When water evaporates, its molecules escape into the air, creating water vapor. As these molecules move around, they collide with each other and with other molecules in the air, exerting a certain amount of pressure.
Water Vapor Pressure Example
How to calculate water vapor pressure?
- First, measure the temperature of the air.
If necessary, convert the temperature into units of Celsius.
- Next, enter the temperature into the formula.
Calculate the water vapor pressure using the temperature from step 1 and the formula above.
- Finally, analyze the results.
Do the results make logical sense? If so, you have your answer, if not, check the calculation.
FAQ
How does temperature affect water vapor pressure?
Temperature has a direct impact on water vapor pressure. As the temperature increases, the kinetic energy of water molecules increases, allowing more water molecules to escape into the air and thus increasing the water vapor pressure. Conversely, as the temperature decreases, the water vapor pressure decreases.
Why is understanding water vapor pressure important?
Understanding water vapor pressure is crucial for various scientific and practical applications, including weather forecasting, the study of climate change, designing HVAC systems, and in industries such as agriculture and food packaging where humidity control is vital.
Can water vapor pressure exceed atmospheric pressure?
In an open atmosphere, water vapor pressure is a component of the total atmospheric pressure (it is the partial pressure of water vapor) and therefore cannot exceed the local total atmospheric pressure. In a sealed or pressurized system, the water vapor partial pressure can rise above 1 atm as temperature increases, increasing the total pressure.
