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### Relevance of Phase Changes

Posted: Sun Feb 02, 2020 5:11 pm
What is the relevance of knowing phase changes? Like, how are they used in calculations?

### Re: Relevance of Phase Changes

Posted: Sun Feb 02, 2020 5:17 pm
If you are calculating the change in enthalpy of a substance and that substance changes phases then it is important to add the energy required by the phase change in order to get an accurate calculation for ΔH.

### Re: Relevance of Phase Changes

Posted: Sun Feb 02, 2020 5:22 pm
You need to take phase changes into account when calculating change of enthalpy in a reaction. The calculations we use assume that all the reactants and products are gases.

### Re: Relevance of Phase Changes

Posted: Sun Feb 02, 2020 8:12 pm
In many of the problems covered in thermo, you have to calculate the energies expelled/absorbed for each part of the phase change, and then add those up to find your enthalpy, $\Delta H$.

### Re: Relevance of Phase Changes

Posted: Sun Feb 02, 2020 8:53 pm
When you are calculating the enthalpy of a reaction, sometimes the reactants or products will be in the liquid form. Since predetermined enthalpy values of elements are usually given in the gas phase, you must add/subtract the enthalpies of the phase changes to these values to determine what they are in a different state so that the overall enthalpy change of the reaction can be calculated.

### Re: Relevance of Phase Changes

Posted: Sun Feb 02, 2020 9:41 pm
When calculating the enthalpy change you need to add the enthalpy as a result of change in temperature as well as the enthalpy that comes from a phase change.

### Re: Relevance of Phase Changes

Posted: Sun Feb 02, 2020 9:46 pm
Since the enthalpy value changes when a substances changes phases, it is necessary to calculate separately the phase change enthalpy and add it to the same-phase reaction enthalpy.

### Re: Relevance of Phase Changes

Posted: Sun Feb 02, 2020 10:50 pm
A phase change would mean that you would have to add the energy required for that phase change in order to calculate the overall enthalpy

### Re: Relevance of Phase Changes

Posted: Sun Feb 02, 2020 11:07 pm
This is important when calculating enthalpy because energy is used for a phase change as well as temperature.

### Re: Relevance of Phase Changes

Posted: Wed Feb 05, 2020 9:39 pm
I think also phase change helps orient what values will be positive and negative. You need to take phase changes into account when calculating the change of enthalpy in a reaction (the calculations we use assume that all the reactants and products are gases).