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Topic: Enthalpy or potential energy?  (Read 4648 times)

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Offline helpmethismakesnosense

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Enthalpy or potential energy?
« on: September 14, 2017, 11:54:15 PM »
Hello

I'm studying Chemistry 12 and something doesn't quite add up.

I'm see quite a lot of graphs like these:

The y axis is labeled as potential energy while the energy difference between the products and the reactants is highlighted as Difference in enthalpy.
Isn't enthalpy supposed to encompass Kinetic energy as well as potential energy? Then how come it is often claimed that the difference there is the difference in enthalpy?
What am I missing?

Offline Vidya

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Re: Enthalpy or potential energy?
« Reply #1 on: September 23, 2017, 06:55:12 AM »
Enthalpy is basically  heat  change during a chemical reaction.Potential energy in a molecule is due to chemical bond  energies and during a chemical change bonds are broken and new bonds are formed.
Do you know that bond breaking is endothermic? why?
Do you know that bond formation is exothermic? why?
First we have to break the bonds of reactants so all energy profiles are going up in the starting of the reaction. Once reactants acquired the minimum amount of the energy required to break bonds (Activation energy),bonds are broken and new bonds for making product start getting formed.This makes the energy profile to move down and difference in energy needed to break the bonds and energy released when new bonds are formed comes out as heat (required or released).
This change is delta H or enthalpy change for the given reaction. 

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