Phase changes

[Andrea_Torres]

How do phase changes affect a reaction? How do they matter?

[Nawal Dandachi 1G]

depending on whether breaking or forming bonds is occurring, you can determine if it's endo or exo.

[J_CHEN 4I]

Phase changes are relevant for problems that want the enthalpy. That is because the energy needed to be supplied for a phase change in a substance is different depending on the current phase of a substance. For example, the energy needed to change a liquid to a gas (the enthalpy of vaporization) is different from the needed to change a solid into a gas (the energy of sublimation).

[Janet Nguy 2C]

You need to account for phase changes in enthalpy problems because the value will be different when the phase changes. This is why you need to calculate separately the enthalpy change from different phases and then add together the enthalpy change from the same phase reaction.