Phase changes

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Abigail Menchaca_1H
Posts: 104
Joined: Sat Sep 07, 2019 12:19 am

Phase changes

Postby Abigail Menchaca_1H » Sun Jan 26, 2020 6:14 pm

How do phase changes play a role in standard enthalpy calculations?

Kate Osborne 1H
Posts: 102
Joined: Fri Aug 30, 2019 12:16 am

Re: Phase changes

Postby Kate Osborne 1H » Sun Jan 26, 2020 6:16 pm

Some of the energy that is used to heat up something is also used to create a phase change, so there could be no measurable change in heat while there was heat absorbed.

MaggieHan1L
Posts: 100
Joined: Thu Jul 11, 2019 12:17 am

Re: Phase changes

Postby MaggieHan1L » Sun Jan 26, 2020 9:32 pm

standard enthalpy changes will be in a certain phase and sometimes you have to add enthalpy of phase changes to calculate enthalpy of reactions.

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

Re: Phase changes

Postby Gerald Bernal1I » Sun Jan 26, 2020 9:41 pm

In order for a phase change to happen enough heat or energy has to be applied to overcome the phase and then the bond. That is why when you use the second method you add the heat of fusion or vaporization to the bond enthalpy to get the enthalpy of the reaction.

Rhea Shah 2F
Posts: 97
Joined: Thu Jul 25, 2019 12:17 am

Re: Phase changes

Postby Rhea Shah 2F » Sun Jan 26, 2020 10:40 pm

Although the temperature of a sample remains the same, heat is being supplied in order to provide the energy needed for a phase change. This is why the heating curve for water is horizontal at times. In calculations, the enthalpy for the phase change must be added to the bond enthalpies in order to get the correct answer.

Eesha Sohail 1D
Posts: 100
Joined: Sat Aug 17, 2019 12:16 am

Re: Phase changes

Postby Eesha Sohail 1D » Sun Jan 26, 2020 10:43 pm

On the heating curve, one axis is temperature, but can someone explain what exactly temperature means on a molecular level vs heat?

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

Re: Phase changes

Postby ABombino_2J » Sun Jan 26, 2020 11:01 pm

Phase changes take up a large amount of heat so although heat is being supplied, the temperature does not change until the threshold for the new phase is reached.

SimranSangha4I
Posts: 99
Joined: Sat Sep 14, 2019 12:17 am

Re: Phase changes

Postby SimranSangha4I » Sun Jan 26, 2020 11:01 pm

The phase would require a certain amount of energy to change. Within enthalpy, the phase change needs to be combined with the bond enthalpy.

Long Luong 2H
Posts: 51
Joined: Thu Sep 19, 2019 12:16 am

Re: Phase changes

Postby Long Luong 2H » Sun Jan 26, 2020 11:10 pm

Eesha Sohail 1D wrote:On the heating curve, one axis is temperature, but can someone explain what exactly temperature means on a molecular level vs heat?

Heat deals with thermal energy, whereas temperature is the molecular kinetic energy (the molecules moving around in the ice/water/vapor).


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