Hess's Law

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Cecilia Jardon 1I
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Joined: Fri Sep 28, 2018 12:16 am

Hess's Law

Postby Cecilia Jardon 1I » Sat Jan 26, 2019 3:59 pm

For Hess's Law do you essentially just manipulate both equations to get the equation that you need and then add both enthalpies?

Schuyler_Howell_4D
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Re: Hess's Law

Postby Schuyler_Howell_4D » Sat Jan 26, 2019 4:11 pm

Pretty much. You can add (or subtract) equations together to get the desired reaction that you need the enthalpy for. Once you have decided what needs to be added or subtracted you use their enthalpies, making sure the signs match if that equation is endo- or exothermic.

Sarah Zhao 4C
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Joined: Fri Sep 28, 2018 12:28 am

Re: Hess's Law

Postby Sarah Zhao 4C » Sat Jan 26, 2019 4:34 pm

Yep, and you can multiple the reaction coefficients and reverse the reaction so they cancel out. Just make sure you do the same to the enthalpy, respectively, multiple them or change the sign.

Chloe Likwong 2K
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Re: Hess's Law

Postby Chloe Likwong 2K » Sat Jan 26, 2019 7:48 pm

Remember to also make sure that the states are the same if you're cancelling.

yuetao4k
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Re: Hess's Law

Postby yuetao4k » Sat Jan 26, 2019 8:32 pm

Yes, make sure that all states of matter can cancel out and then manipulate each equation (multiplying or flipping) so that you get the final equation. Add together the enthalpies to find the enthalpy of the reaction.

maldonadojs
Posts: 57
Joined: Fri Sep 28, 2018 12:27 am

Re: Hess's Law

Postby maldonadojs » Sat Jan 26, 2019 8:51 pm

Yes that is the basics. The two strategies are to either flip the equations or multiply them by whole numbers. If you do decide to flip the equation you must make sure that you change the sign of the enthalpy. (I believe that is how you spell it)


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