Do we still use heat of fusion when going from a liquid to a solid?

[HopefulMDclass2020]

Hello, pretty simple question, I just could not seem to find an answer when I was searching.

I know during a phase change from solid to liquid we use q=m * delta H (vap/fusion depending on the process).
However, would we still use that equation when going from a liquid to a solid, since it is in a lower energy state, it should require less energy.

Thanks in advance!

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[m25]

Yes, it should be the same, except you add minus sign since it's just going the other way around.

 

[lifetothefullest]

However, would we still use that equation when going from a liquid to a solid, since it is in a lower energy state, it should require less energy.

Also, think of it this way - it's not just that it requires "less" energy to go the other way. It actually has to require the opposite amount of energy. Why? Because if you take something and melt it, you're releasing energy. To get that energy back into the thing you melted, you're going to need to put in exactly as much as was lost earlier from melting. That's just conservation of energy. That's why it's exactly opposite in sign.

 

[plusalpha]

Also, think of it this way - it's not just that it requires "less" energy to go the other way. It actually has to require the opposite amount of energy. Why? Because if you take something and melt it, you're releasing energy. To get that energy back into the thing you melted, you're going to need to put in exactly as much as was lost earlier from melting. That's just conservation of energy. That's why it's exactly opposite in sign.

If you're melting something (fusion), you're actually putting IN energy/heat... the opposite process (crystallization) results in release of energy/heat.