Standard Reaction Enthalpy

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205389184
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Joined: Sat Sep 07, 2019 12:18 am

Standard Reaction Enthalpy

Postby 205389184 » Sun Jan 26, 2020 8:25 pm

How do you calculate the standard reaction enthalpy if the bond enthalpies are not available? Can you please include an example too

jisulee1C
Posts: 149
Joined: Thu Jul 25, 2019 12:17 am

Re: Standard Reaction Enthalpy

Postby jisulee1C » Sun Jan 26, 2020 9:16 pm

If the bond enthalpies are not available you can calculate the standard reaction enthalpy using the standard enthalpy of formation of all products and subtracting that from the standard enthalpy of formation of all reactants.

Amy Xiao 1I
Posts: 101
Joined: Sat Jul 20, 2019 12:15 am

Re: Standard Reaction Enthalpy

Postby Amy Xiao 1I » Sun Jan 26, 2020 9:22 pm

jisulee1C wrote:If the bond enthalpies are not available you can calculate the standard reaction enthalpy using the standard enthalpy of formation of all products and subtracting that from the standard enthalpy of formation of all reactants.


To add on to that, Dr. Lavelle talked about this being the third method to calculate enthalpy, other than using Hess's Method and using bond enthalpies. This is the formula: ΔH°RXN = ΣΔHf° (Products) - ΣΔHf° (Reactants), which is what jisulee explained above- that you take the sum of the standard enthalpy of formation for products and subtracting the sum of those for reactants from it.

Sofia Barker 2C
Posts: 101
Joined: Wed Sep 18, 2019 12:21 am

Re: Standard Reaction Enthalpy

Postby Sofia Barker 2C » Sun Jan 26, 2020 11:30 pm

If bond enthalpies are unavailable, use values of standard enthalpy of formation. The sum of the standard enthalpy of formation of all products subtracted by the sum of the standard enthalpy of formation of all reactants involved in the reaction will give you the total change in enthalpy.

For the example he gave in class, he multiplied the moles of each reactant and product by their associated standard enthalpy of formation when calculating the total enthalpy of the reaction so keep that in mind! For example, if one product was 2H2O (l), then 2 would be multiplied by H20's standard enthalpy of formation and then that value would be added to the equivalent value of the other products in that specific reaction.


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