Question

Must the amount of heat absorbed as 1 kg of saturated liquid water boils at 100 °C, be equal to the amount of heat released as 1 kg of saturated water vapor condenses at 100 °C? Why? Which process requires more energy: completely vaporizing 1 kg of saturated liquid water at 1 atm pressure or completely vaporizing 1 kg of saturated liquid water at 8 atm pressure? Why? A food-scientist is cooking three identical beef stews in pans that are (a) uncovered, (b) covered with a light lid, and (c) covered with a heavy lid. For which case will the cooking time be shortest? Why? a. b. c.

Answer 1

a. Heat of vaporization is exactly equal to the heat of condensation.

b. Vaporizing 1 kg of water at 8 atm will require more heat than at 1 atm as boiling point depends directly on atmospheric pressure.

c. Cooking takes more time in open container as heat is consumed in doing work against surrounding also, hence here cooking time will be shortest in a container covered with a heavy lid and longest in open lid container.