I have read in this article ( https://www.tlv.com/global/TI/steam-theory/steam-heating-mechanism.html ) that :

The latent heat contained in steam is released the instant steam condenses into the liquid state. The amount of latent heat released is 2 to 5 times greater than the amount of sensible heat available from hot water (saturated water) after condensation.

But why is that ?


Imagine you move two strong magnets together. At some point, their attraction is strong enough that they snap together with a ‘click’. Their rapid motion becomes sound and heat.

Steam condensing is like that. The water molecules snap together to form the liquid and I n the process liberating energy that shows up as heat.

Why is it larger? The heat of motion is (generally) smaller than the energy from the “snap” together because that defines the critical temperature: above that, the thermal motion breaks apart the links to make vapor. Below that temperature, there’s less energy and the molecules tend to stay together as liquid.

Water’s a bit more complicated due to its shape, but this is the basic idea.

  • $\begingroup$ Thank you @Bob :) so to make sure that I have understood it well; can I think about it as because the heat of motion of gas is much greater than that of liquid , so when changing from gas to liquid the latent heat released would be the difference between the two heat motions and since the difference is big then we can say that the latent heat is larger than the sensible heat ? $\endgroup$
    – user65035
    Aug 4 '18 at 20:32
  • 1
    $\begingroup$ @hellothere that’s a bit tricky. The heat of translational motion of the water molecules in gas at 100C is the same as liquid at 100C; each mode has 1/2kT. (The magnets in the example would keep jittering around) What’s liberated is the energy of attraction $\endgroup$ Aug 4 '18 at 20:43

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