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calculating standard gibbs free energy of reation

Posted: Mon Jan 25, 2016 12:08 pm
by Rachael_1H
Calculate standard gibbs free energy of a reaction for the reaction showing the decomposition of mercury (II) oxide at 298 K.

2HgO(s)---> 2Hg(l) + O2(g)

Standard reaction enthalpy of formation for HgO = -90.83
standard molar entropy HgO=70.29, Hg=76.02, and O2=205.14

When finding the standard gibbs free energy of this rxn, I believe that the answer key in our practice quiz booklet changes the Standard RXN Enthalpy of formation of HgO= +90.83

Why is the Standard RXN Enthalpy of formation of HgO made positive?

Re: calculating standard gibbs free energy of reation

Posted: Mon Jan 25, 2016 12:25 pm
by Fariha Hameed 1D
You make the value positive because you are not forming HgO but rather doing the reverse, which is decomposing 2HgO to make 2Hg and O2. Hope this helps!