the vapour pressure of water at 20 degree celcius is 18 mm hg .if the relative humidity is 35 % the weight per litre of air at 20 degree celcius is ?
To calculate the weight per liter of air at 20 degrees Celsius, given the relative humidity (RH) and the vapor pressure of water, you can use the concept of partial pressure.
Step 1: Calculate the partial pressure of water vapor in the air.
The vapor pressure of water at 20 degrees Celsius is given as 18 mmHg. Since the relative humidity (RH) is given as 35%, this means the air contains 35% of the maximum amount of water vapor it could hold at 20 degrees Celsius.
To calculate the partial pressure of water vapor, multiply the RH by the vapor pressure of water:
Partial pressure of water vapor = RH * Vapor pressure of water
Partial pressure of water vapor = 35% * 18 mmHg = 0.35 * 18 mmHg = 6.3 mmHg
Step 2: Calculate the partial pressure of dry air.
The sum of partial pressures of all components in a mixture is equal to the total pressure. In this case, the total pressure is the atmospheric pressure at 20 degrees Celsius, which is around 760 mmHg.
The partial pressure of dry air is then calculated by subtracting the partial pressure of water vapor from the total pressure:
Partial pressure of dry air = Total pressure - Partial pressure of water vapor
Partial pressure of dry air = 760 mmHg - 6.3 mmHg = 753.7 mmHg
Step 3: Convert the partial pressure of dry air to weight per liter.
To convert the partial pressure of dry air to weight per liter, you need to use the ideal gas law, which states that at STP (Standard Temperature and Pressure), 1 mole of gas occupies 22.4 liters of volume.
Therefore, the weight of air per liter is calculated by multiplying the partial pressure of dry air by the molar mass of dry air (approximately 29 g/mol) and dividing by the molar volume at STP (22.4 liters/mol):
Weight per liter of air = (Partial pressure of dry air * Molar mass of dry air) / Molar volume at STP
Weight per liter of air = (753.7 mmHg * (29 g/mol)) / (22.4 liters/mol)
Weight per liter of air ≈ 978.34 g
Therefore, the approximate weight per liter of air at 20 degrees Celsius, with a relative humidity of 35%, is 978.34 grams.