Question

Why steam at 100 degrees Celsius is better for heating purposes than water at 100 degrees Celsius?​

Answer 1

Explanation:

The short answer is because temperature is not a measure of energy, whereas heat is energy (it may seem counterintuitive, but 10kg of ice at -5 Celsius contains more heat that a roofing nail glowing red-hot). We do measure the energy (heat) required to raise the temperature of a substance and call this measure heat capacity. Different materials have different heat capacities. When a material cools down, the same amount of heat energy is released (and we get warm from it in this case).

So, to your specific question, the water requires an amount of energy to get to 100 C (~4186J/kg.K) and this is all the energy available to warm us up as the water cools back down. However, to change the water from liquid phase to steam phase, we need to input extra energy to "separate the molecules" (nice way to think about it). This is called the latent heat of vapourisation and is a huge amount compared to the energy required to simply raise the temp by a degree (~2260kJ/kg). All this energy is 'absorbed' by the water as it changes to steam without raising its temperature at all (once it's fully steam any extra energy input will then increase the temperature of the steam). So as this steam changes back to liquid water, all this massive amount of heat is released and we get very warm.

In figures, 1 gram of water cooling from 100C down to 20C would yield ~335J of energy, whereas 1 gram of steam at 100C (exactly the same amount of water and at the same temperature, but in a different phase) condensing to liquid then cooling to 20C would yield ~2595J of energy.

Answer 2

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Steam has got more energy stored in it. It is the latent heat of vaporization, 540 calories per gram.

In addition to this, steam is pressurized and its temperature goes still higher. Steam is more fluent than water. Water heats what ever is immersed in it. Steam is like air. It covers the object from all sides and heat it.

Steam can do mechanical work also which hot water cannot do. Now a days electricity is used, so this point is not so valid.

Only in house hold water can be used not in industries.