Pure water vapour is trapped in a vessel of volume 10 ml. The relative humidity is 40%. The vapour is compressed slowly and isothermally. The volume of vapour (in ml) at which first drop of liquid wil

Question

Pure water vapour is trapped in a vessel of volume 10 ml. The relative humidity is 40%. The vapour is compressed slowly and isothermally. The volume of vapour (in ml) at which first drop of liquid will form, is

TestHub · Accepted Answer

RH = 40% means vapour pressure = 0.40 x p_sat. On slow isothermal compression the vapour pressure rises (Boyle: p ∝ 1/V) until it reaches p_sat; the first liquid drop then appears.

p1V1 = p_sat V2: 0.40 p_sat × 10 = p_sat x V2 ⇒ V2 = 4 ml.

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