Final answer:
The heat required to vaporize 1 kg of a substance and the heat given off during condensation can be measured using the heat of vaporization and heat of condensation respectively. These values are specific to each substance and represent the amount of heat energy needed to change from liquid to vapor and vice versa.
Step-by-step explanation:
The heat required to vaporize 1 kg of a substance is known as the heat of vaporization. This is the amount of heat energy needed to change the substance from the liquid phase to the vapor phase. Similarly, the heat given off by 1 kg of a substance when condensing is also known as the heat of condensation. These values are specific to each substance and can be measured in different units, such as kilojoules per kilogram (kJ/kg) or kilocalories per kilogram (kcal/kg).
For example, when 1 mol of water at 100°C and 1 atm pressure is converted to 1 mol of water vapor at 100°C, 40.7 kJ of heat is absorbed from the surroundings. When 1 mol of water vapor at 100°C condenses to liquid water at 100°C, 40.7 kJ of heat is released into the surroundings.