Enthalpy sign changes

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EmmaShahabi1L
Posts: 11
Joined: Wed Sep 21, 2016 2:55 pm

Enthalpy sign changes

Postby EmmaShahabi1L » Thu Jan 12, 2017 1:06 pm

When using bond enthalpy values or simply just plugging in enthalpy values, when do you change the sign of the value before summating the equation? For reference, number 59 of the chapter 8 homework.

Tom Notcovich 3B
Posts: 13
Joined: Wed Sep 21, 2016 2:58 pm

Re: Enthalpy sign changes

Postby Tom Notcovich 3B » Thu Jan 12, 2017 1:29 pm

Using bond enthalpies to calculate the change in enthalpy we know that when bonds are formed they release energy and will have a negative (-) value. Basically, change the products to negative and keep the reactants positive. Ref. page 16 of the course reader.

Jenny_Thompson_3I
Posts: 25
Joined: Wed Sep 21, 2016 2:59 pm

Re: Enthalpy sign changes

Postby Jenny_Thompson_3I » Thu Jan 12, 2017 3:49 pm

For a reaction that is exothermic it will have a negative enthalpy since it is releasing energy. A reaction that is endothermic will have a positive enthalpy since it is absorbing energy.


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