How much heat is required to make one kg of steam?
To arrive at the answer to the question, we have to consider:
a. Pressure at which water is to be heated.
b. Initial temperature of the water.
c. Amount of super-heat required.
From the above, we will calculate the enthalpy change of water in this process. And calculate actual heat required to produce steam of requisite quality considering the efficiency of the heating process.
But considering the standard conditions, we can derive the answer as follows.
To make one kg of steam, we need one kg of water. Let’s assume water be at room temperature of say 20° C. There will be no loss of heat in heating the water from 20°C to its boiling point of 100° C.
Saturated steam is steam, which is produced at boiling temperature. At 100° C, both water and steam can exist. The heat required to heat 1 kg (1000 grams) of water is 80,000 calories considering the specific heat 1 calorie required per gram per 1°C rise of temperature. 80,000 calories of heat required to rise of temperature of 80° C (from 20° C to 100° C, 1000 X 1 X 80 calories = 80,000 calories).
Raising the temperature of the steam above the saturation temperature (which is called super-heating) also requires the addition of more heat. The hotter you make the steam, the more heat you need.
So in standard conditions, the total heat required = 80,000 calories + 5,40,000 calories = 6,20,000 calories of heat i.e., 620 kilo calories.