Hess's Law

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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?

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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
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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
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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
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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
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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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