Enthalpy versus heat

isochoric/isometric:
isothermal:
isobaric:

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Sanjana Borle 2K
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Enthalpy versus heat

Postby Sanjana Borle 2K » Thu Feb 06, 2020 3:41 pm

For enthalpy and heat, the only differences between them (q and H) is that enthalpy is a state property and the heat is not, correct? When are we supposed to assume that they equal each other?

chemboi
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Joined: Sat Jul 20, 2019 12:16 am

Re: Enthalpy versus heat

Postby chemboi » Thu Feb 06, 2020 5:23 pm

I think they equal each other when there is no work being done on the system. Enthalpy is the change in heat of a system at constant pressure, and yes it is a state function vs. heat which depends on the path of the reaction.

205291012
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Joined: Mon Nov 11, 2019 12:17 am

Re: Enthalpy versus heat

Postby 205291012 » Thu Feb 06, 2020 10:12 pm

yes, that is correct.
delta H = q when no work is done. So assume they're the same when no work is being done by or on the system.

Erik Buetow 1F
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Re: Enthalpy versus heat

Postby Erik Buetow 1F » Sun Feb 09, 2020 8:19 pm

Yes, in essence that is the only difference. A general rule of thumb is that enthalpy is always heat, but heat does not always equal enthalpy. This has to do with the fact that enthalpy is heat at a constant pressure, so if it is not a constant pressure then heat will not equal enthalpy.

Cavalli_1H
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Re: Enthalpy versus heat

Postby Cavalli_1H » Sun Feb 09, 2020 8:25 pm

enthalpy is a form of heat but heat is not a form of enthalpy

Charysa Santos 4G
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Re: Enthalpy versus heat

Postby Charysa Santos 4G » Sun Feb 09, 2020 8:29 pm

Delta H is equal to q + w, so when there is no work being done on or by the system (or when w = 0), then delta H = q

SarahCoufal_1k
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Re: Enthalpy versus heat

Postby SarahCoufal_1k » Sun Feb 09, 2020 8:40 pm

In the review session today they said enthalpy is always heat, but heat is not always enthalpy. The definition of enthalpy is heat at constant pressure. So if it isn't at constant pressure, the heat can't be described as enthalpy

kausalya_1k
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Re: Enthalpy versus heat

Postby kausalya_1k » Sun Feb 09, 2020 11:29 pm

so enthalpy is basically like heat but only during isobaric (deltaP=0) situations
basically, enthalpy is always heat, but heat is not always enthalpy.

William Francis 2E
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Re: Enthalpy versus heat

Postby William Francis 2E » Sun Feb 09, 2020 11:42 pm

I think it should be noted that enthalpy can never really be determined. When pressure is constant, ΔH=q, so the change in enthalpy is equal to heat, but enthalpy itself is not equal to heat.

William Francis 2E
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Re: Enthalpy versus heat

Postby William Francis 2E » Sun Feb 09, 2020 11:46 pm

Also, I believe that ΔU is equal to q+w, not ΔH, so when no work is being done on or by a system, it doesn't necessarily mean that ΔH=q. Rather, ΔH=q under constant pressure conditions. When no work is being done by a system, ΔH=q+PΔV as derived from ΔH=ΔU+PΔV with (q+w) substituted for ΔU and w=0.

Leila_4G
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Re: Enthalpy versus heat

Postby Leila_4G » Tue Feb 11, 2020 10:58 am

And to further clarify, standard enthalpy for a reaction and heat needed for that reaction are the same, right? As long as the q is for the same number of moles at the delta H is for.
Because I noticed that standard enthalpy only has the units of kJ (or J). (Not kJ per mol)

Sartaj Bal 1J
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Re: Enthalpy versus heat

Postby Sartaj Bal 1J » Sat Feb 15, 2020 2:23 pm

Enthalpy is the study of heat released or absorbed in chemical reactions and physical changes. It is considered a state property as its value is determined by its current state. Heat is the transfer of energy due to temperature differences. It depends on the path taken and is therefore not a state property.


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