4. Does a mole always have the same mass?

No

Explanation:

different atoms do not have the same mass therefore a mole of one thing is not the same as a mole of another thing.

Because different molecules and atoms do not have the same mass, one mole of one thing does not weigh the same as one mole of something else. Atoms and molecule mass is measured in amu. One amu is equal to one gram per mole. This means that if an atom has a mass of one amu, one mole of this atom weighs one gram.

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 !

the maximum mass of nh3 is nh3 in grams