Free Energy Question

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Joined:Mon Feb 20, 2017 8:53 am
Free Energy Question

Post by George » Thu Mar 09, 2017 10:42 am


Hydrogen peroxide can be prepared in several ways. One method is the reaction between hydrogen and oxygen, another method is the reaction between water and oxygen. Given the ΔG°rxn values for each reaction, which method (reaction 1 or 2) requires less energy under standard conditions?

1. H2(gas) + O2(gas) <---> H2O2(liquid) ΔG°rxn = -120.4 kJ
2. H2O(liquid) + 1/2 O2(gas) <---> H2O2(liquid) ΔG°rxn = +116.7 kJ

Would the answer be reaction 2 because it is lower in magnitude? I know that a negative free energy value indicates a spontaneous reaction and a positive value a nonspontaneous reaction but is the sign significant in this case?

ΔG = ΔG° + RTln(Q)
ΔG = -72.6 kJ + (0.008314 kJ mol- K-)(298 K)(ln 32.4)
ΔG = -72.6 + 8.6174 = -63.98 kJ

I am not sure about my approach to this question. Can anyone confirm if I am on the right track?
Thanks. All help Is very much appreciated.

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