Heat vs. Enthalpy

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Matthew Lee 3L
Posts: 51
Joined: Fri Sep 29, 2017 7:07 am

Heat vs. Enthalpy

Postby Matthew Lee 3L » Thu Jan 18, 2018 5:51 pm

What is exactly is the difference between heat and enthalpy?

Sarah_Stay_1D
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Joined: Sat Jul 22, 2017 3:00 am
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Re: Heat vs. Enthalpy

Postby Sarah_Stay_1D » Thu Jan 18, 2018 5:58 pm

Matthew Lee 3L wrote:What is exactly is the difference between heat and enthalpy?


Enthalpy is the study of heat released or absorbed in chemical reactions and physical changes. Heat is a type of energy which can be transferred from one object to another. Heat transfer is the result of highly energized atoms or molecules colliding with less energized atoms or molecules. Energy is then transferred to the less energized (more slowly moving) particle and it subsequently speeds up. When a system is at constant pressure the heat released or absorbed is equal to the change in enthalpy.

JamesAntonios 1E
Posts: 70
Joined: Fri Sep 29, 2017 7:04 am

Re: Heat vs. Enthalpy

Postby JamesAntonios 1E » Thu Jan 18, 2018 6:27 pm

Enthalpy is heat but not heat is enthalpy.

Vincent Tse 1K
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Re: Heat vs. Enthalpy

Postby Vincent Tse 1K » Thu Jan 18, 2018 7:01 pm

To add on/consider:

Enthalpy is a state function in which when you know the beginning and end states, you'll know the change in enthalpy; whatever happens in the "middle" doesn't matter. On the other hand, heat does depend on the "path" taken between those beginning and end states. Sarah said it right: enthalpy is the measure of energy in a process (which includes heat, internal energy, work, etc), while heat an energy transfer within that process.

Dylan Mai 1D
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Joined: Sat Jul 22, 2017 3:00 am

Re: Heat vs. Enthalpy

Postby Dylan Mai 1D » Thu Jan 18, 2018 8:05 pm

so when using delta H, is it wrong for someone to refer to that as heat? delta H is enthalpy right?

JamesAntonios 1E
Posts: 70
Joined: Fri Sep 29, 2017 7:04 am

Re: Heat vs. Enthalpy

Postby JamesAntonios 1E » Tue Jan 23, 2018 8:39 pm

Dylan Mai 1D wrote:so when using delta H, is it wrong for someone to refer to that as heat? delta H is enthalpy right?

Heat and enthalpy are only equal when pressure is constant and volume is constant. That is why Dr. Lavelle wrote the equation qp=delta H. If these are not constant, you have to assume that Delta U=Delta H + PdeltaV...


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