## when to change sign of enthalpies

405318478
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Joined: Sat Jul 20, 2019 12:16 am

### when to change sign of enthalpies

Hi, i'm looking at question 4 on the Pizza Rolls review sheet. When do I know to change the sign of the enthalpies given?

Eugene Chung 3F
Posts: 142
Joined: Wed Nov 15, 2017 3:03 am

### Re: when to change sign of enthalpies

If you mean question 4a, you would flip the sign if u flip the chemical equation.

Rida Ismail 2E
Posts: 139
Joined: Sat Sep 07, 2019 12:16 am

### Re: when to change sign of enthalpies

For a Hess’s law equation anything you do to the chemical equation you need to do to the Delta H as well

Ariana Iranmahboub1G
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Joined: Fri Aug 09, 2019 12:17 am

### Re: when to change sign of enthalpies

If you are using the reverse reaction, you would flip the sign of delta H.

205154661_Dis2J
Posts: 109
Joined: Wed Sep 18, 2019 12:21 am

### Re: when to change sign of enthalpies

If you mean 4A, we change the sign of enthalpies when we reverse the equation. For example, we reversed equation 2 because we wanted Vodka on the product side since we have it on the product side in the overall recipe. We then multiplied it by two since we want 2 Vodka on the product side to match the 2 Vodka in the overall recipe. I hope that makes sense!

Posts: 116
Joined: Thu Jul 25, 2019 12:15 am

### Re: when to change sign of enthalpies

Flipping the sign accounts for flipping the equation because we have changed from an endo to exo or exo to endo rxn.

Micah3J
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Joined: Tue Oct 08, 2019 12:16 am

### Re: when to change sign of enthalpies

By flipping the equation it would mean that you are just taking the reverse reaction instead right? So then basically the reactants are on the products side in order to cancel things out?

Amy Kumar 1I
Posts: 114
Joined: Thu Jul 11, 2019 12:15 am

### Re: when to change sign of enthalpies

Yes, taking the reverse reaction allows the products and reactants to switch sides so that things can get canceled out as needed.

Return to “Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)”

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