Hess's Law

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torialmquist1F
Posts: 49
Joined: Sat Jul 22, 2017 3:00 am

Hess's Law

Postby torialmquist1F » Tue Jan 23, 2018 12:05 pm

When using Hess's law to calculate enthalpy, can you eliminate a molecule within the same equation? For example, if one of the equations has CO2 on both sides can they be crossed out?

RyanS2J
Posts: 32
Joined: Thu Jul 27, 2017 3:00 am

Re: Hess's Law

Postby RyanS2J » Tue Jan 23, 2018 12:47 pm

When adding two chemical equations using Hess' Law, identities such as CO2 that appear on both sides can indeed be crossed out, provided they are in equal quantities.

104922499 1F
Posts: 53
Joined: Fri Sep 29, 2017 7:04 am

Re: Hess's Law

Postby 104922499 1F » Tue Jan 23, 2018 5:03 pm

they can be crossed out if they are of equal amounts

Jennie Fox 1D
Posts: 66
Joined: Sat Jul 22, 2017 3:01 am

Re: Hess's Law

Postby Jennie Fox 1D » Tue Jan 23, 2018 6:38 pm

The molecules must be on opposite sides and I=equal in quantity to be able to fully cancel them out. For example, if there are 2 modes of CO2 on the reactant side of one equation ands you are adding this equation to one in which there are 2 moles of CO2 on the product side, the CO2's will cancel out.

Evelyn L 1H
Posts: 67
Joined: Fri Sep 29, 2017 7:05 am

Re: Hess's Law

Postby Evelyn L 1H » Wed Jan 24, 2018 12:08 am

To make things cancel out more easily, you can switch the products and reactants. All you would have to do is switch the sign of delta H.

Phillip Winters 2F
Posts: 50
Joined: Fri Sep 29, 2017 7:05 am

Re: Hess's Law

Postby Phillip Winters 2F » Wed Jan 24, 2018 12:13 am

If the two molecules are on opposite sides of the equation in equal amounts, then they can be canceled out because nothing is changing from reactants to products


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