<p>[AP</a> Central - Units in Thermochemical Calculations](<a href=“Supporting Students from Day One to Exam Day – AP Central | College Board”>Units in Thermochemical Calculations – AP Central | College Board)
Is this really in the AP Chemistry test?</p>
<p>Yes although the page makes it look more complicated than it really is. Just add the formation energy for all products (while multiplying the coefficient from the balanced equation for each product with its formation energy) - the same idea with the reactants.</p>
<p>Usually just 1 or 2 questions involving it and the reason it works can be shown pretty easily with Hess’s law.</p>