Calculating standard enthalpy  [ENDORSED]

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Jacquelyn Hill 1
Posts: 41
Joined: Sat Jul 22, 2017 3:01 am

Calculating standard enthalpy

Postby Jacquelyn Hill 1 » Sun Mar 11, 2018 4:44 pm

Between the two methods for calculating the change in standard enthalpy (using "products - reactants" or using the provided bond ethalpy values), why don't they result in the same answer?

Thu Uyen Tran 1B
Posts: 31
Joined: Fri Sep 29, 2017 7:05 am

Re: Calculating standard enthalpy  [ENDORSED]

Postby Thu Uyen Tran 1B » Sun Mar 11, 2018 4:48 pm

The bond enthalpies are averages therefore, they are less accurate. This leads to different answers, but the numbers should not be too far from one another.

Paula Dowdell 1F
Posts: 72
Joined: Tue Nov 15, 2016 3:00 am

Re: Calculating standard enthalpy

Postby Paula Dowdell 1F » Sun Mar 11, 2018 5:00 pm

Standard formation enthalpy refers to the formation of a compound from elementary compounds, while bond energy is applicable when considering the formation of a molecule from isolated atoms.

Sandhya Rajkumar 1C
Posts: 50
Joined: Fri Jun 23, 2017 11:40 am

Re: Calculating standard enthalpy

Postby Sandhya Rajkumar 1C » Mon Mar 12, 2018 2:19 pm

The bond strength between a given pair of atoms varies slightly from one compound to another because of the different electronegativities of the other atoms in the compound. When we use bond enthalpy values to calculate standard enthalpy, we are actually using the mean bond enthalpy which is the average value of bond enthalpy calculated from different molecules containing the bond. So this method may be slightly less accurate than using "products - reactants"

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