(a) what is the vapor pressure of water at 20.0ºc ? (b) what percentage of atmospheric pressure does this correspond to? (c) what percent of 20.0ºc air is water vapor if it has 100% relative humidity? (the density of dry air at 20.0ºc is 1.20 kg/m3 .)

a). Vapour pressure = 2333.141 Pa

b). Percentage of atmospheric pressure = 99 %

c). Percentage of water vapour = 1.4 %

Explanation:

a). From water saturation pressure table,

Vapour pressure of water at 20°C is 17.5 torr

We know, 1 torr = 133.322 Pa

Therefore, 17.5 torr = 2333.141 Pa

Therefore, vapour pressure at 20°C is 2333.141 Pa

b). At 20°C, the pressure at atmospheric unit = 0.0231 atm

                                                                           = 0.0231 x Pa

                                                                          = 2310 Pa

Therefore,

             = 0.99

Therefore percentage of atmospheric pressure = 0.99 x 100

                                                                                 = 99 %

c). We Know

Relative Humidity (Rh)=

where is vapour pressure

Rh is given as 100% = 1

∴ 1 =

  = 2333.141 Pa

Now humidity ratio is

  , where is mass of vapour

                                                                    is mass of air

Let the total pressure be Pa

Therefore, percentage of water vapour is 0.01485 x 100

                                                                  = 1.4 %