## Relevance of Phase Changes

Alice Chang 2H
Posts: 101
Joined: Fri Aug 30, 2019 12:18 am

### Relevance of Phase Changes

What is the relevance of knowing phase changes? Like, how are they used in calculations?

J Medina 2I
Posts: 102
Joined: Wed Sep 25, 2019 12:17 am

### Re: Relevance of Phase Changes

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.

William Francis 2E
Posts: 101
Joined: Wed Sep 18, 2019 12:20 am

### Re: Relevance of Phase Changes

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.

Emily Burghart 1k
Posts: 50
Joined: Wed Sep 18, 2019 12:17 am

### Re: Relevance of Phase Changes

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, $\Delta H$.

Sydney Pell 2E
Posts: 100
Joined: Wed Sep 11, 2019 12:17 am

### Re: Relevance of Phase Changes

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.

ABombino_2J
Posts: 102
Joined: Thu Jul 11, 2019 12:15 am

### Re: Relevance of Phase Changes

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.

Janet Nguy 2C
Posts: 115
Joined: Sat Aug 24, 2019 12:17 am

### Re: Relevance of Phase Changes

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.

Trent Yamamoto 2J
Posts: 111
Joined: Sat Aug 17, 2019 12:18 am

### Re: Relevance of Phase Changes

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

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

### Re: Relevance of Phase Changes

This is important when calculating enthalpy because energy is used for a phase change as well as temperature.

Megan Kirschner
Posts: 46
Joined: Wed Feb 20, 2019 12:17 am

### Re: Relevance of Phase Changes

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).