How many moles of Al are used to form 509.8 g of Al2O3?

1019.6 moles of Al.

Explanation:

4Al +3O2 → 2Al2O3

You have 509.8 g moles of Al2O3. While balancing the equation, you got 2 moles of Al2O3 and 4 moles of Al,

so "4 mol Al gives 2 mol Al2O3

After you cancel out the units of measurement to check the order of the conversion, multiply 509.8 g with 4 and then divide the answer by 2.

.= (509.8 x 4) / 2

=  2039.2 / 2

= 1019.6 moles of Al.

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.