How do I solve this heat of formation problem?

Question

3Al (s)+3O2 (g)===> 2AlO3 (s) ΔH= -3351kJ

How do I calculate the change in enthalpy in kJ for the formation of 65.0 g of Al2O3?

Answer 1

I see you are listing a series of questions, so instead of doing them all for you, I'll guide you.  Hope that's ok.

 

First of all, the equation you have written is not correct. It should be 4Al(s) + 3O₂(g) ==>2Al₂O₃(s)

Here you are given the heat of reaction (enthalpy) when FOUR moles of Al react to form TWO moles of Al₂O₃.

The question now asks for the enthalpy when you form 65.0 g of Al₂O₃.  So, convert that mass to moles.  Once you know the moles of Al₂O₃, you can calculate the enthalpy to produce that amount based on the fact that it takes 3351 kJ to make 2 moles.