taking phase change into account

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Payton Kammerer 2B
Posts: 49
Joined: Tue May 01, 2018 3:00 am

taking phase change into account

Postby Payton Kammerer 2B » Sun Feb 02, 2020 11:57 pm

I am a little bit confused about when the phase change needs to be taken into account in enthalpy change calculations. I have written in my notes that it is only necessary to include the phase change when there are gases involved. Why is this the case?

Tanmay Singhal 1H
Posts: 143
Joined: Sat Jul 20, 2019 12:16 am

Re: taking phase change into account

Postby Tanmay Singhal 1H » Sun Feb 02, 2020 11:57 pm

you need to account for the amount of energy required to actually shift from one phase to another. ice has a specific heat capacity and water has one. it accounts for the transition state

Deepika Reddy 1A
Posts: 125
Joined: Thu Jul 11, 2019 12:15 am

Re: taking phase change into account

Postby Deepika Reddy 1A » Mon Feb 03, 2020 12:09 am

A phase change can be between solids and liquids or liquids and gases. It takes a certain amount of energy for the phase to change.

Gerald Bernal1I
Posts: 102
Joined: Thu Jul 11, 2019 12:16 am

Re: taking phase change into account

Postby Gerald Bernal1I » Mon Feb 03, 2020 12:52 am

Phase change is taken into account when the matter is changing phase. For examples if a problem asks to find the energy from boiling water when you started at a certain temperature. You would calculate q=mc(Tf-Ti) and use the specific heat and then add the heat of vaporization energy which does not have a temperature change and uses heat of vaporization rather than specific heat.

805422680
Posts: 103
Joined: Sat Sep 14, 2019 12:16 am

Re: taking phase change into account

Postby 805422680 » Mon Feb 03, 2020 1:02 am

it is taken into account when energy is first required to change the state of matter and then heat the new phase. therefore for example the heating of water from ice takes into account the energy required to melt the ice and then raise the temperature of water.

Sanjana K - 2F
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Joined: Sat Sep 07, 2019 12:17 am
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Re: taking phase change into account

Postby Sanjana K - 2F » Mon Feb 03, 2020 2:12 am

Also, in addition to what is being said above, something to remember: whenever you're dealing with phase changes, you have to calculate the heat required in 2 different steps. For example, if you're trying to go from a block of ice at 0 degrees to water at 50 degrees, you first need to find the heat of fusion for the 0 degrees ice to melt to 0 degrees water and then in the next step, find the heat to get from 0 degrees water to 50 degrees water.


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