When to use which method for calculating reaction enthalpies

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904936893
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Joined: Fri Sep 28, 2018 12:29 am

When to use which method for calculating reaction enthalpies

Postby 904936893 » Mon Jan 28, 2019 9:15 pm

How do you know which of the three methods to use when given a specific problem? Like when would you use Hess's Law vs. Bond Enthalpies vs. Standard Enthalpies of formation?

405161024
Posts: 36
Joined: Fri Sep 28, 2018 12:25 am

Re: When to use which method for calculating reaction enthalpies

Postby 405161024 » Mon Jan 28, 2019 9:23 pm

I think it depends on what values are given in the problem. But also I think Hess's law is more accurate than bond and standard enthalpies so if you can do either I would do Hess's

Christina Chang 1C
Posts: 34
Joined: Thu May 10, 2018 3:00 am

Re: When to use which method for calculating reaction enthalpies

Postby Christina Chang 1C » Mon Jan 28, 2019 11:23 pm

Do you know which equation to use for question 8.9 in the 6th edition textbook? I'm not sure which equation uses those variables.

Tatum Keichline 2B
Posts: 64
Joined: Fri Sep 28, 2018 12:26 am

Re: When to use which method for calculating reaction enthalpies

Postby Tatum Keichline 2B » Tue Jan 29, 2019 1:10 am

for 8.9, use 8.206e-2Latm/kmol and 8.314J/kmol then convert to kJ and subtract that answer from kJ given.

Elias Omar 1G
Posts: 52
Joined: Fri Sep 28, 2018 12:17 am

Re: When to use which method for calculating reaction enthalpies

Postby Elias Omar 1G » Tue Jan 29, 2019 2:24 am

Bond Enthalpies: Generally you do not want to use this method as it is unreliable. I'm actually not totally sure when you'd use this method.

Hess's Law: Remember Hess's Law is about adding enthalpies. You'll use this in problems involving the enthalpies of multiple reactions.

Standard Enthalpies: You'll need to use this method in pretty much any problem involving enthalpies at some point, as standard enthalpies are a part of calculating the overall enthalpies in a reaction, since each substance in a particular state has one.


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