Chemistry - Ideal Gas Question with Solution | TestHub
Temperature and relative humidity of air are 27°C and 75% on a certain day. Vapour pressure of water at 27°C and 7°C are 24.0 mm and 8.4 mm Hg, respectively. If the fraction of the mass of water vapour that will condense, if the temperature falls to 7°C, is x, then the value of 1000x is
Answer:
Solution:
Partial pressure of water vapour at 27°C: p1 = 0.75 × 24.0 = 18.0 mm Hg. For a fixed amount of air, moles of vapour per unit volume are proportional to p/T. Before cooling: n1/V proportional to 18.0/300 = 0.06. After cooling to 7°C (280 K) the vapour is saturated (the initial vapour is more than enough, since 8.4/280 < 18/300), so n2/V proportional to 8.4/280 = 0.03. Fraction of vapour mass remaining = 0.03/0.06 = 1/2, so fraction condensed x = 1 - 1/2 = 0.5. Hence 1000x = 0500.
