Phase Changes

[kiara chan]

Can someone please explain to me again why the enthaply of sublimation is equal to the enthalpy of fusion and vaporization?

[Triston Dinh 1D]

The enthalpy of fusion measures the change in energy when a substance changes state from a solid --> liquid. The enthalpy of vaporization measures the change in energy when a substance changes state from a liquid --> gas.

Enthalpy of sublimation measures the change in energy when a substance changes state from a solid --> gas. Thus, you can simply add the enthalpy of fusion and vaporization together to find the enthalpy of sublimation since the change in states goes from solid -> liquid -> gas. Ultimately, using this equation, you are still just measuring change in energy from solid --> gas.

[Kurosh Zamiri 1I]

Hi! The enthalpy of sublimation can be thought of as the change in enthalpy of a gas - the change in enthalpy of a solid, since sublimation involves a phase change from solid to a gas.

The enthalpy of fusion involves the change in enthalpy of a liquid - the change in enthalpy of a solid, since fusion implies the change from a solid to a liquid.

The enthalpy of vaporization involves the change in enthalpy of a gas - the change in enthalpy of a liquid, since vaporization is the phase change from liquid to gas.

Putting these equations together gives us:

Change in enthalpy of a liquid - change in enthalpy of a solid + change in enthalpy of a gas - change in enthalpy of a liquid. Thus, the change in enthalpy of the liquid cancels, leaving us with:

Change in enthalpy of a gas - the change in enthalpy of a solid. This proves that the enthalpy of sublimation is equal to the enthalpy of fusion and vaporization. Hope this helps!

[805401611]

When we looking at enthalpy, we know that it is a change in state, so the enthalpy of sublimation deals with the change of solid to vapor/gas. Now, since this change starts like the enthalpy of fusion (solid) and ends like the enthalpy of vaporization (gas), we can assume that when we add these two enthalpies together, they will equal the enthalpy of sublimation. Hope that helps!

[Jonathan Shyu 3L]

Sublimation is the change of a substance from a solid phase directly to a gas phase. Thus, simply put, it is kind of like going from solid to liquid, then liquid to gas. Solid to liquid is called fusion, and liquid to gas is called vaporization. When you combine the enthalpy of fusion with the enthalpy of vaporization, you get sublimation.

[Emily Engelkemier 1E]

During sublimation, a solid goes directly to a gas. Since enthalpy is a state function, it must be additive, so we can add the enthalpy of fusion (solid to liquid) and the enthalpy of vaporization (liquid to gas) to get the enthalpy of sublimation.

[Melody Khoshneviszadeh 3C]

enthalpy of sublimation is equal to the enthalpy of fusion and vaporization because sublimation indicates that the substances have undergone a phase change from solid to gas which is when broken down is just the sum of the enthalpy for solid to liquid(fusion) and then liquid to gas(vaporization). sublimation combines these 2 phase changes into one term but really is just the 2 processes combined so by adding the 2 enthalpies we get the total enthalpy for the process of sublimation.

[HemangD 3K]

Here's how to approach your question algebraically:

change in enthalpy of vaporization = enthalpy in a vapor state - enthalpy in a liquid state
change in enthalpy of fusion = enthalpy in a liquid state - enthalpy in a solid state

change in enthalpy of sublimation = (change in enthalpy of vaporization) + (change in enthalpy of fusion)
change in enthalpy of sublimation = (enthalpy in a vapor state - enthalpy in a liquid state) + (enthalpy in a liquid state - enthalpy in a solid state)
change in enthalpy of sublimation = enthalpy in a vapor state - enthalpy in a liquid state + enthalpy in a liquid state - enthalpy in a solid state
change in enthalpy of sublimation = enthalpy in a vapor state - enthalpy in a solid state

Hope this helps!

[Aaron Martinez]

The enthalpy of sublimation is equal to the enthalpy of fusion and vaporization because enthalpy can be added and subtracted from itself easily. And since the enthalpy of fusion is solid to liquid, and the enthalpy of vaporization is liquid to gas, the enthalpy of sublimation is sold to gas, so you can add the two together.