Bond Enthalpies

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Riya Sood 4G
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Bond Enthalpies

Postby Riya Sood 4G » Tue Jan 28, 2020 8:36 am

Why is calculating enthalpy from bond enthalpies considered to be not as efficient as other methods?

McKenna_4A
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Re: Bond Enthalpies

Postby McKenna_4A » Tue Jan 28, 2020 8:58 am

Because each bond enthalpy AVERAGES can be found on a table. The bond enthalpy of a specific bond depends on the molecule it is in (electrons may be shared unequally). Therefore, using average bond enthalpies will provide an inaccurate value.

Marni Kahn 1A
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Re: Bond Enthalpies

Postby Marni Kahn 1A » Tue Jan 28, 2020 9:09 am

It is also important to take into consideration that some reactions require a change in enthalpy due to a phase change in addition to the substances' bond enthalpies. In this way, Hess's method is more efficient and not as time costly because the enthalpy changes are already given.

Katie Bart 1I
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Re: Bond Enthalpies

Postby Katie Bart 1I » Tue Jan 28, 2020 11:45 am

Is calculating enthalpy from bond enthalpies more accurate?

Paul Hage 2G
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Re: Bond Enthalpies

Postby Paul Hage 2G » Tue Jan 28, 2020 11:53 am

Bond enthalpies of diatomic molecules (Br2, I2, Cl2, N2, O2, H2, F2) are accurate because they are measured for those specific molecules; however, all other bond enthalpies are averages from many different molecules, so they are not completely accurate.

005384106
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Re: Bond Enthalpies

Postby 005384106 » Tue Jan 28, 2020 12:22 pm

For Friday’s lecture when we talked about bond enthalpies, are the energy values for each product and reactant going to be given? How can we solve for these values?

Jialun Chen 4F
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Re: Bond Enthalpies

Postby Jialun Chen 4F » Tue Jan 28, 2020 1:11 pm

I agree with McKenna. Due to the numbers given in the bond enthalpy chart being averages, this method is not as accurate relatively.

Michelle Xie 2B
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Re: Bond Enthalpies

Postby Michelle Xie 2B » Tue Jan 28, 2020 4:54 pm

The bond enthalpies are averages of all the possible ones, so it is less accurate.

Shivam Rana 1D
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Re: Bond Enthalpies

Postby Shivam Rana 1D » Tue Jan 28, 2020 6:03 pm

Using this method is less accurate and takes longer because all the bonds need to be broken and reformed. It is less accurate because the bond enthalpies are averages, not exact values.

Leila_4G
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Re: Bond Enthalpies

Postby Leila_4G » Tue Jan 28, 2020 7:51 pm

Is the table we find this in the textbook or is there a general one online that is the same?

alicechien_4F
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Re: Bond Enthalpies

Postby alicechien_4F » Tue Jan 28, 2020 8:19 pm

Leila_4E wrote:Is the table we find this in the textbook or is there a general one online that is the same?


I would go with the table in the textbook for homework problems because sometimes the bond enthalpies differ slightly online. It should be roughly the same.

Emily Chirila 2E
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Re: Bond Enthalpies

Postby Emily Chirila 2E » Tue Jan 28, 2020 8:30 pm

More accurate methods include Hess’s Method (adding rxns to obtain net rxn) or using ΔH°values from a table


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