Need help with Hess law problem cant come up with third equation?

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Answer 1 · 2018-04-04T05:54:35

Just add the chemical equations together as you would linear equations....and in fact these are linear equations....

And so....

#N_2(g) + O_2(g) rarr 2NO(g)# #;DeltaH^@=180.6*kJ*mol^-1#.

#2NO(g) + O_2(g) rarr 2NO_2(g)# #;DeltaH^@=-114.2*kJ*mol^-1#.

And their sum...

#cancel(2NO(g)) + O_2(g)+N_2(g) + O_2(g) rarr 2NO_2(g)+cancel(2NO)#

To give...#N_2(g) + 2O_2(g) rarr 2NO_2(g)# s required..

#DeltaH_"overall"^@=(180.6-114.2)*kJ*mol^-1=66.4*kJ*mol^-1#.