Adding Enthalpy of Phase Changes

[Olivia D 3B]

What exactly does it mean to "add enthalpy of phase changes for liquids and solids"? Could someone possibly provide an example of when this is necessary and how to do so?

Thanks in advance!

[Katie Shi 1F]

When doing bond enthalpy problems, the tables of bond enthalpies we will use refer to breaking bonds in gases. When looking at bonds in liquids or solids, these will have different bond enthalpies than the same compounds in their gaseous phase. Therefore, if we want to find the bond enthalpy of a liquid you would need to add deltaH_vap and deltaH of the given bond enthalpy from the table. If we want to find the bond enthalpy of a solid you would need to add deltaH_sub and deltaH of the given bond enthalpy from the table.

[Elaine Steinberg 3H]

Whenever you want to find the bond enthalpy of non-gas substance, you'll have to consider the additional enthalpy of phase changes since the bond enthalpy table gives values specifically referring to substances' gas form.

[905695298]

So the bond table only provides values of gases. We need to also consider liquid and solid as well. So you want to add Hvap or Hsub in addition to the gases.