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


Moderators: Chem_Mod, Chem_Admin

Harjas Sabharwal 1G
Posts: 42
Joined: Sat Jul 22, 2017 3:01 am

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

Postby Harjas Sabharwal 1G » Mon Jan 15, 2018 6:52 pm

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
Posts: 31
Joined: Sat Jul 22, 2017 3:00 am
Been upvoted: 1 time

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

Postby Jakob von Morgenland 2C » Mon Jan 15, 2018 7:07 pm

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
Posts: 32
Joined: Sat Jul 22, 2017 3:00 am

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

Postby torieoishi1A » Thu Jan 18, 2018 1:41 pm

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
Posts: 51
Joined: Thu Jul 13, 2017 3:00 am

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

Postby Michael Cheng 1C » Fri Jan 19, 2018 6:03 pm

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

Remi Lathrop 1G
Posts: 51
Joined: Fri Sep 29, 2017 7:07 am

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

Postby Remi Lathrop 1G » Fri Jan 19, 2018 8:30 pm

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.


Return to “Concepts & Calculations Using First Law of Thermodynamics”

Who is online

Users browsing this forum: No registered users and 1 guest