High-yield concept: Phase Changes

[SaintJude]

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Can someone please explain conceptually why sublimation would absorb heat?

Which one of the following processes will absorb heat from the surroundings ?

A. Sublimation
B. Freezing
C. Condensation
D. Deposition

I see that only A is going from an "orderly" to --> less orderly .....

 

[chiddler]

first, we understand that sublimation is solid to gas, right?

Atom---BOND---Atom ----energy----> Atom ---------------- atom

to break bond, we have to add energy

that energy, of course, comes from the surrounding. therefore, surrounding energy = temperature decreases as sublimation occurs.

conversely, reforming the bond releases energy. to help understand, think about what happens when a very unstable species reacts and becomes very stable. a lot of energy is released, right?

 

[MedPR]

You have to heat up an ice cube to get it to melt, right? So when ice melts, it is absorbing heat. Conceptually you should expect solid --> gas to require the same enthalpy change as solid --> liquid, just a higher magnitude. So if melting absorbs heat, sublimation should as well.