Cho 10,2 gam hỗn hợp A gồm Mg và Al phản ứng vừa đủ với dung dịch H2SO4 19,6%, sau phản ứng thu được 11,2 lit H2( đktc) a. Tính % khối lượng mỗi kim loại trong A.
b. Tính khối lượng dung dịch H2SO4 cần dùng.

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 !