Renyijc
156536460205373538854069813631.jpg textbook pg 98 how come they divide by 4?
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BedokFunlandJC
Because as given in the question (always be careful to pay attention to the coefficients of the equation for the topic of energetics!), delta H = -1260 kJ/mol is for 4 mol of NH3 as stated in the equation.

Hence, per 1 mol of NH3, delta H = -1260 / 4 = -315 kJ/mol

Note that the /mol units for delta H isn't referring to per mol of any specific species (eg. NH3), but per mol of the equation as written, so to speak.
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Renyijc
Okay thank you🙂 
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