1. How many moles of tin are needed to react with 3.5 moles of hydrogen fluoride?

1.75 mole of Sn

Explanation:

We'll begin by writing the balanced equation for the reaction. This is given below:

Sn + 2HF —> SnF2 +H2

From the balanced equation above,

1 mole of Sn reacted with 2 moles of HF.

Therefore, Xmol of Sn will react with 3.5 moles of HF i.e

Xmol of Sn = 3.5/2

Xmol of Sn = 1.75 mole

Therefore, 1.75 mole of Sn is needed to react with 3.5 moles of HF

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 !