Phase change enthalpy signs

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rkang00
Posts: 69
Joined: Fri Sep 28, 2018 12:25 am

Phase change enthalpy signs

Postby rkang00 » Sat Jan 26, 2019 5:21 pm

For phase change enthalpies, do we have to change signs for them as well depending on which side of the rxn they're on?

emily gao 1C
Posts: 61
Joined: Fri Sep 28, 2018 12:29 am

Re: Phase change enthalpy signs

Postby emily gao 1C » Sat Jan 26, 2019 5:49 pm

yes bc exothermic is - and endothermic is +.

freezing: exothermic: delta h is negative
melting: endothermic: delta h is positive

Helen Zhao 1F
Posts: 31
Joined: Fri Sep 28, 2018 12:20 am

Re: Phase change enthalpy signs

Postby Helen Zhao 1F » Sat Jan 26, 2019 7:26 pm

When you freeze something, the heat from the object is absorbed into the surroundings and as a result, the total heat in the system is lost. When heat is lost, enthalpy becomes more negative. When you melt something, heat is added into the object and the total heat of the system is increased. Enthalpy increases and becomes more positive.


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