Subtopic: Psychrometry – properties of air-water vapour mixture
Question Statement:
Molecular masses of water and air are 18.02 and 28.97 kg·(kg mol)⁻¹, respectively. Air in a room is at 40 °C under a total pressure of 101.3 kPa absolute and contains water vapour at a partial pressure of 4.0 kPa. If saturated vapour pressure of water at 40 °C is 7.37 kPa, the relative humidity of this air in per cent is ______. [round off to 2 decimal places]
Official Answer Key:
52.00 to 54.50
Step-by-Step Solution & Explanation
Relative Humidity = (partial pressure of water vapour / saturation vapour pressure) × 100 = (4.0/7.37) × 100 = 54.27%. (The molecular masses given are distractors relevant to computing humidity ratio/humid volume, not RH.)
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