Standard Enthalpy of Formation

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Cindy Ngo 1E
Posts: 14
Joined: Fri Jul 22, 2016 3:00 am

Standard Enthalpy of Formation

Postby Cindy Ngo 1E » Thu Jan 12, 2017 9:43 pm

Why is it that the standard enthalpy of formation of a product can be a negative value? Can it be a positive value?

AndrewM2G
Posts: 9
Joined: Fri Jul 22, 2016 3:00 am

Re: Standard Enthalpy of Formation

Postby AndrewM2G » Thu Jan 12, 2017 9:56 pm

It is my understanding that standard enthalpies of formation can have both negative and positive values because it indicates the heat involved in the reaction that forms a substance. A negative enthalpy of formation implies that the formation releases heat, and a positive enthalpy of formation implies that the formation process takes up energy from its surroundings.

stephanieyang_3F
Posts: 62
Joined: Wed Sep 21, 2016 2:55 pm

Re: Standard Enthalpy of Formation

Postby stephanieyang_3F » Thu Jan 12, 2017 10:00 pm

You can think back to the idea that as new bonds form, energy is released and when bonds are broken, energy is required. The standard enthalpy of formation is the net amount of energy that is either released or absorbed per mole of a product in a particular reaction. The majority of the standard enthalpy of formation values are negative because a negative amount of energy correlates to how stable the product actually is.

There are some positive values of standard enthalpy of formation, but I think it's rare.


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