Straightaway, thank you for providing this website in that I can see I will frequent its url ad infinitum owing to my inaugural science regimen!
That said, here we go...
1) I understand the equation to find the enthalpy of a reaction, H of rxn= H of products - H of reactants. Yet the following question does not offer the H of formation for the first reactant. Is this unusual? My chapter's practice questions had all values, so I do not understand.
C2H4 (g) + 3O2 (g) ---> 2CO2 (g) + 2H2O (L)
2(-313.5) + 2(-285.
- (0 + ?)
Am I missing something?
2) CaCo3 (s) --> CaO (s) + CO2 (g)
Calculate the change in enthalpy if 66.8g of CO2 are formed.
So I am dealing with 1.52 mol of CO2, which I multiplied by -393.5 (heat of formation of CO2) resulting in -598 KJ/mol.
So -635.6 + -598 = -1234KJ/mol
CaCo3 heats of formation = -1206.9 KJ/mol
So I found the difference = 27.1KJ/mol; however, the book says 2.70 X 10^2
I do not see my oversight.
Many sincere thanks to ya'll!
As an aside, my experience with chemistry thus far has been frustrating insofar as I thoroughly read the chapter, follow along with the practice questions yet, when I enter the end of chapter problem sets, I get 1/5 correct. I am using Chang's 9th edition. I do not get it.