1. The problem statement, all variables and given/known data 20 litres of moist air at 25 degrees celsius with a relative humidity of 75% are compressed isothermally to a volume of 4 litres. Calculate the mass of water condensed? (One method, find the original water vapour pressure, it will be increased by what factor?) 2. Relevant equations pV= mRT water vapour pressure = density x R x T 3. The attempt at a solution Where should I start with this problem. Finding the mass is really hard here, the mass of water condensed is only part a of the question. if i had that, i could figure it all out. any hints in the right direction?