Question

How do you balance `Al + F_2 -> AlF_3`?

Answer 1

`Al + F_2 rarrAlF_3`
here F is unbalanced : on right hand side(product side) there are 3 F and on the left hand side there is 2F

use the L.C.M of the two numbers to balance on both sides
here L.C.M of (2,3)=6
so we try to get six F on both sides

`Al + 3F_2 rarr 2AlF_3`
now we need to balance Al
`2Al +3F_2 rarr2AlF_3`

Answer 2

You balance it stoichiometrically: GARBAGE IN MUST EQUAL GARBAGE OUT.

Explanation:

A chemical reaction ALWAYS CONSERVES MASS AND CHARGE:

`2Al(s) + 3F_2(g) rarr 2AlF_3(s)`.

Is mass conserved in this representation? How? If you have to do calculations with this formula, to make it a little easier on yourself you could write:

`Al(s) + 3/2F_2(g) rarr AlF_3(s)`

What does `1/2F_2(g)` represent in `"grams"`?