Question

Water is being heated in a vertical piston-cylinder device. the piston has a mass of 20 kg and a cross-sectional area of 100 cm2. if the local atmospheric pressure is 100 kpa, determine the temperature at which the water starts boiling.

Answer 1

Answer: We have pressure from the weight of the piston + atmospheric pressure acting on the gas pressure from the piston... P = F / area = mass x acceleration due to gravity / area P = (24 kg x 9.80 m/s²) / (90 cm² x (1m/100cm)²) = 26133 N/m² = 2.61x10^4 Pa = 26.1 kPa total pressure acting on the gas = 26+85 kPa = 111 kPa then.. via clausius clapeyron equation.. ln(P1 / P2) = (dHvap / R) x (1 / T2 - 1 / T1) and if I pick say.. the normal boiling point of water for P2, T2.. then... P1 = 111 kPa P2 = 101.325 kPa dHvap = 40680 J/mole R = 8.314 J/moleK T2 = 373.15 K T1 = ?? ---> T1 = 102.46°