How many grams of the excess reactant are left over according to the reaction below given that you start with 10.0 g of al and 19.0 grams of o2?
reaction: 2al+ 3o2 → 2al2o3

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !

it is stable as it is in group 0 which have full outer shells of electrons