## Difference between heat(q), internal energy(U), and enthalpy(H)

$\Delta U=q+w$

Harjas Sabharwal 1G
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Joined: Sat Jul 22, 2017 3:01 am

### Difference between heat(q), internal energy(U), and enthalpy(H)

I don't understand the conceptual difference between heat(Q), internal energy(U), and enthalpy(H). I understand that from a mathematical standpoint U contains Q but I am confused as to what exactly the difference is.

Jakob von Morgenland 2C
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### Re: Difference between heat(q), internal energy(U), and enthalpy(H)

The internal energy is the system's total storage of energy; heat is the amount of energy transferred; enthalpy is a measurement of energy (also has to be held at a constant pressure in order to be a state function).

torieoishi1A
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Joined: Sat Jul 22, 2017 3:00 am

### Re: Difference between heat(q), internal energy(U), and enthalpy(H)

Heat(Q): the transfer of energy between a system temp. and its surrounding temperature. It can go in either direction, but is transferred from high temperature to low temperature. An object, itself, does not possess heat.
Internal energy (U): the total amount of energy stored in a system. For a closed system, it is the sum of the heat(q) and work (w). For an isolated system, it is equal to 0 because nothing is exchanged with its surroundings.
Enthalpy (H): sum of total internal energy and the product of pressure and volume

Michael Cheng 1C
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Joined: Thu Jul 13, 2017 3:00 am

### Re: Difference between heat(q), internal energy(U), and enthalpy(H)

So then, what is the difference between heat (q) and enthalpy (H)? more specifically the difference between q and deltaH

Remi Lathrop 1G
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Joined: Fri Sep 29, 2017 7:07 am

### Re: Difference between heat(q), internal energy(U), and enthalpy(H)

To answer the most recently asked question on this thread, heat (q) is simply a measure of the energy released or absorbed by a system. Enthalpy (∆H) is very similar except it measures the heat released or absorbed at a constant pressure.
Just q does not necessarily imply that the reaction is at constant pressure, but in order to find enthalpy it must be.