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Posted: Thu Jan 11, 2018 5:07 pm
by Ashley Macabasco 2K
For Hess's law, do you only add the enthalpy changes of the same phase to find the standard reaction enthalpy? For example in question 8.59 to calculate the standard reaction enthalpy of 4HNO3(l) + 5N2H4(l) ---> 7N2(g) + 12H2O(l), nitrogen is not included in finding the standard reaction enthalpy and I was wondering if it was due to it being in the gas phase and not the liquid phase as the other components of the equation.

Re: 8.59

Posted: Thu Jan 11, 2018 5:11 pm
by Ramya Lakkaraju 1B
From what I understand, the only reason that nitrogen is not included is because its enthalpy is 0 if you look at the table. I don't think it has to do with the fact that it is in its gas phase.

Re: 8.59

Posted: Thu Jan 11, 2018 5:39 pm
by Gevork 2E
From my understanding, Nitrogen has its value as 0 because in standard conditions it will be diatomic. It would not require any energy loss or gain to be in that state, so therefore its value is 0.