Answer
Product: $AlF_3(s)$
Balanced equation:
$2Al(s) + 3F_2(g) --\gt 2AlF_3(s)$
Work Step by Step
1. In a combination reaction, two compounds/elements combine to form a single product.
$A + B --\gt AB$
Therefore, the product must be something like: $AlF$. But, the charge of aluminum is equal to $+3$, therefore, there must be 3 fluorines to balance the charge.
Product: $AlF_3(s)$
Complete equation:
$Al(s) + F_2(g) --\gt AlF_3(s)$
2. Balance the number of fluorines, by putting a "2" on $AlF_3$, and a "3" on $F_2$.
$Al(s) +3F_2(g) --\gt 2 AlF_3(s)$
3. Balance the number of aluminum atoms, by putting a "2" in the front of $Al$:
$2Al(s) + 3F_2(g) --\gt 2AlF_3(s)$
