How do I solve change in enthalpy problems like this?

Question

3. 2Al(s) + 3O2(g) -----> 2Al2O3(s) enthalpy change is -3351 kJ
What would be the enthalpy change (in kJ) for the formation of 65.0 g of Al2O3(s)?
a) -251000
b) -126000
c) -2464
d) -1232

Answer 1

Your balanced equation is, once again, incorrect.  You have 2 Al on the left side and 4 on the right side.  

 

(1) determine how many moles Al₂O₃ is equivalent to 65.0 g

(2) From knowing that 2 moles Al₂O₃ is equal to -3351 kJ, you should be able to figure out the kJ equal to the 65 g.