## Phase change

$\Delta U=q+w$

Riya Sood 4G
Posts: 160
Joined: Sat Aug 24, 2019 12:18 am

### Phase change

is the delta H positive or negative when ice turns to liquid?

Suraj Doshi 2G
Posts: 100
Joined: Fri Aug 02, 2019 12:15 am

### Re: Phase change

This phase change causes the change in enthalpy to be positive (delta H is positive).

MinuChoi
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Joined: Wed Sep 18, 2019 12:15 am

### Re: Phase change

Enthalpy will be positive because the molecules must absorb energy to loosen forces on each other and assume more free form.

Dina Marchenko 2J
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Joined: Thu Jul 25, 2019 12:16 am

### Re: Phase change

A positive delta H means energy is put in (endothermic) which is what is necessary to break the bonds that holds a solid together into a liquid. That's why change in enthalpy is positive.

faithkim1L
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Joined: Fri Aug 09, 2019 12:17 am

### Re: Phase change

Delta H should be positive.

John Liang 2I
Posts: 102
Joined: Fri Aug 30, 2019 12:18 am

### Re: Phase change

Because the phase change requires energy, there is a + delta H value. Hope this helps

KHowe_1D
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### Re: Phase change

Delta H would be positive because the molecules are absorbing energy to "loosen" the bonds.

Callum Guo 1H
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### Re: Phase change

Naneeta Desar 1K
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Joined: Fri Aug 09, 2019 12:15 am

### Re: Phase change

Delta H is positive since melting is breaking bonds and energy is required in order to do so.

Celine 1F
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### Re: Phase change

In this case, delta H is positive

Abigail_Hagen2G
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### Re: Phase change

It would be positive, because it requires energy to cause the phase change.

Isabella Dal Porto 1H
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Joined: Fri Aug 30, 2019 12:16 am

### Re: Phase change

Breaking the bonds that are holding the solid together requires energy. Thus, delta H is positive since the reaction is endothermic (needs energy/energy absorbed).

KSong_1J
Posts: 101
Joined: Thu Jul 11, 2019 12:17 am

### Re: Phase change

Delta H is positive because energy must be used to break the bonds to turn ice into a liquid

Anish Natarajan 4G
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Joined: Thu Jul 25, 2019 12:16 am

### Re: Phase change

You're going from a state of lower energy to a state of higher energy when you go from a solid to a liquid (or a liquid to a gas) so the change in enthalpy should be positive

gconcha
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### Re: Phase change

Because heat (energy) needs to be added to the ice in order to make it undergo a phase change into liquid form, $\Delta H$ is positive

Anushka Chauhan2B
Posts: 51
Joined: Sat Aug 24, 2019 12:16 am

### Re: Phase change

It should be positive

205389184
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Joined: Sat Sep 07, 2019 12:18 am

### Re: Phase change

Delta H would be positive when ice turns to liquid

Nare Nazaryan 1F
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Joined: Fri Aug 09, 2019 12:17 am

### Re: Phase change

Delta H is positive when ice turns to liquid (applying heat to change from solid to liquid).

smurphy1D
Posts: 51
Joined: Mon Nov 18, 2019 12:18 am

### Re: Phase change

Delta H is positive because heat is being added in order to melt the ice

Posts: 102
Joined: Tue Oct 02, 2018 12:16 am

### Re: Phase change

Delta H is positive as the system absorbs energy in order to go to a liquid phase AND the energy remains there to keep it in a liquid phase.

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

### Re: Phase change

A positive delta H means energy is put in, which makes it endothermic, which is what is necessary to break the bonds that holds a solid together into a liquid. That's why the change in enthalpy is positive!