Answer:
2AlF3 + 3Mg -> 3MgF2 + 2Al
Step-by-step explanation:
_AlF3 + _Mg -> _MgF2 + _Al
Start with the more complex molecule. Lets use AlF3.
Assign a "1" toAlF3:
1AlF3 + _Mg -> _MgF2 + _Al
This brings in 1 Al and 3 F atoms, so lets add coefficients to use them up on the product side:
1AlF3 + _Mg -> 1.5MgF2 + 1Al
Note that the coefficient for MgF2 is 1.5. The coefficients have to be whole numbers, but we'll come back to this later. Lets balance the other atoms first.
The 1.5MgF2 means we need 1.5Mg on the reactant side:
1AlF3 + 1.5Mg -> 1.5MgF2 + 1Al
This is balanced, but we need to correct the molecules having 1.5 as their coefficients. We can simply double each component:
2AlF3 + 3Mg -> 3MgF2 + 2Al
This looks balanced: Element Reactants Products
F 6 6
Al 2 2
Mg 3 3