## Equation Choice

605110118
Posts: 75
Joined: Wed Sep 18, 2019 12:21 am

### Equation Choice

What defines a phase change and how does that relate to which equation you use?

AKhanna_3H
Posts: 104
Joined: Wed Sep 18, 2019 12:19 am

### Re: Equation Choice

A phase change is when something goes from a solid to liquid (fusion), liquid to gas (vaporization), solid to gas (sublimation), or the reverse of these.
In terms of equations to use, I assume you are talking about finding the q value, or amount of heat, associated for that phase change. In this case you would use the equation q = m*deltaH, for which m = mass and deltaH = change of enthalpy for the phase change (ex: deltaH of fusion).

AronCainBayot2K
Posts: 101
Joined: Fri Aug 30, 2019 12:17 am

### Re: Equation Choice

Phase change occurs when a molecule/reaction goes from solid to liquid, liquid to gas, etc. This denotes fusion, vaporization, in terms of change in enthalpy. We learned equations: Hvap=Hvap-Hliq and Hfus=Hliq-Hsol and Hsub=Hvap-Hsol which relate to phase changes.

KnarGeghamyan1B
Posts: 102
Joined: Fri Aug 09, 2019 12:15 am

### Re: Equation Choice

Remember that if the phase change involves the atoms becoming more free and moving faster (i.e. solid to liquid, liquid to gas) the process is endothermic because the system is gaining heat and energy, meaning the q value is positive. The opposite is true for exothermic processes.

Alondra
Posts: 36
Joined: Tue Feb 26, 2019 12:15 am

### Re: Equation Choice

Phase changes: solid --> liquid (fusion), liquid --> gas (vaporization), solid --> gas (sublimation) or vice versa : melting, condensation, deposition.

Attachments u18l2b3.gif (4.82 KiB) Viewed 100 times

WGaines_2E
Posts: 47
Joined: Mon Nov 18, 2019 12:18 am

### Re: Equation Choice

the most common phase changes are melting/freezing (dHf) and evaporating/condensing (dHv)