Assalamualaikum,
Based on the previous chapter , I've learned on how to calculating the specifc heat of entalphy on non reactive process. I learned on how to applying hypothetical path , watson corellation and how to interpret data from the pyscometric chart .
Next , i've learned about the balances on reactive process where it required me to understand the concept heat of reaction , heat of reaction and HESS law and quite frankly , from all chapter in (PCP II ), this chapter is the chapter that i love the most because it play with a lot of molar things. .In other words , it mean that it required me to do a lot of atomic balance and i love to do atomic balances . So throughout this chapter , what i can say is , an energy balances on a reactor tell the process engineer how much heating or cooling the reactor requires in order to operate at the desired conditions. It show how entalphy changes that accompany chemical reaction are determined from tabulated phsical propeties of the reactant and products and how calculated entalpies if reaction are incoporated in energy balances on reactive processes. About the heat of formation and heat of reaction , both this reaction were a method that you can choose in order to finding the specific entalphy Q. What differentiate both of this method was the equation used and the formula. To put in another word , heat of formation basically is a formation reaction of a compound in which the compound is formed from its constituentselement as they normally occur . For example the formation of CO2 (C(s) + O2(g) --------> CO2(g) ) and the heat of formation of this reaction is -393.5 kj/mol ( from table B1) and the formula for heat of formation can be seen in page 447 (9.3-1). For the heat of reaction , it is about the entalphy changes for a process in which stoichiometric quantities of reactant at temperature T and pressure P react completely in a single reaction to product at the same temperature and pressure.
To summarize , when performing energy balances on a reactive process, two procedures( two method) maybe followed in the calculations of H . The choices is in your hand, you can choose in which method you prefer , but this doesnt mean you to specialize in only one method . Sometimes question may asked you to do for both method but don't worry as long you do the exercise given by Dr. Azeman , insyaAllah , everything gonna work out just fine .