The vapor pressure is the pressure of the vapor phase of a substance when it is
ID: 1836716 • Letter: T
Question
The vapor pressure is the pressure of the vapor phase of a substance when it is in equilibrium with the solid or liquid phase of the substance. The relative humidity is the partial pressure of water vapor in air divided by the vapor pressure of water at that same temperature, expressed as a percentage. If the amount of water vapor in the air is kept constant as the air is cooled, a temperature is reached, called the dew point, at which the partial pressure and vapor pressure coincide and the vapor is saturated. If the air is cooled further, vapor condenses to liquid until the partial pressure again equals the vapor pressure at that temperature. The table below lists the vapor pressure of water at various temperatures.
On a spring day in the mid-western United States, the air temperature at the surface is 28.0°C. Puffy cumulus clouds form at an altitude where the air temperature equals the dew point (see information above). If the air temperature decreases with altitude at a rate of 0.6 C°/100 m, at approximately what height above the ground will clouds form if the relative humidity at the surface is 35% and 80%? (Hint: Use the above table.)
Explanation / Answer
surface temp = 28 degC
RH = 30%
SVP at 28 degC = 3.78e+3
actual vapour pressure at the surface = 3.78e+3*0.3 = 1.134e+3 Pa
This is the SVP below 10 degC.
temp. falls by 0.6 deg per 100 m
temp diff 28-10 = 18 degC.
height h = (18/0.6)* 100 = 3000 m. cloud fromatio occurs above 300 m.
RH = 80%
vapour pressure = 3.78e+3*0.8 = 3.024e+3 Pa
SVP at 24 C = 2.99 e+3 Pa
SVP at 26 C = 3.36e+3 Pa
T = 24+(2/0.37)*0.03 = 24.16 degC , at this temp the cloud formation will happen as this is the SVP temp. for 3.024e+3 PA
altitude = ((28.0 - 24.6)/0.6)*100 = 640m height where SVP temp is reached and cloud formation will happen.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.