Posted by Taylor Marie on .
Given: 2Al2O3 (s) 4Al (s) + 3O2 (g) °H = 3351.4 kJ, what is °H for the formation of 12.50 g of aluminum oxide?
Help please.

College Chemistry 
Taylor Marie,
Never i got it :).

College Chemistry 
GK,
The deltaH for the decomposition of 1 mole of Al2O3 is half of 351.4 kJ since the chemical equation shows 2 moles of Al2O3.
Convert 12.50g Al2O3 to moles by dividing it by the molar mass of Al2O3. Multiply your answer by 351.4kJ to get the enthalpy of decomposition of 12.50g Al2O3.
The deltaH of formation is the inverse of the enthalpy of decompositin. Attach a negative sign to the previous answer.