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How to Calculate Water Vapor Temperature

Since vapor is the gaseous form of water, it obeys the Ideal Gas law, which expresses the relationship between the pressure (P), volume (V), mass (m) and temperature (T) of a gas using a value called the individual gas constant (R). The value of R varies according to the gas and the system of units used to measure the variables. Water vapor's individual gas constant is 461.5 if the equation uses metric units or 2,760 if it uses imperial units.

Instructions

- 1
  Substitute the vapor's pressure, volume, mass and individual gas constant into the Ideal Gas Law: pV = mRT.
  
  For example, if p equals 100 kilopascals, V equals 1,260.59 cubic meters and m equals one kilogram, the equation becomes: 100(1,260.59) = 1(461.5)T.
- 2
  Divide each side of the equation by mR to isolate T.
  
  100(1,260.59)/1(461.5) = T
- 3
  Simplify the equation to find the value of T. This is the approximate temperature in degrees Kelvin.
  
  T = 273.15 K
- 4
  Substitute the Kelvin temperature into the Celsius or Fahrenheit equation and simplify to convert the answer to one of those temperature scales.
  
  Celsius = Kelvin - 273.15
  
  Fahrenheit = 1.8 * (Kelvin - 273.15) + 32
  
  For example, 273.15 K equals 0 degrees Celsius or 32 degrees Fahrenheit.

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