Step 1: Balance the equation
We have _Cu + _BaCl2 --> _Ba + _CuCl3.
To balance out the chlorine, we would need to double the CuCl3 and triple the BaCl2, resulting in the following equation:
_Cu + 3BaCl2 --> _Ba + 2CuCl3
Now, the Ba and Cu are no longer balanced! To do that, we would need to double the Cu and triple the Ba, resulting in the following equation:
2Cu + 3BaCl2 --> 3Ba + 2CuCl3
Now the equation is balanced!
Step 2: Convert grams Ba to moles Ba.
We do this using the molar mass!
4.35 g Ba x 1 mol Ba/ 137.327g Ba = 0.0317 moles of Ba
Step 3: Convert moles Ba to moles BaCl2
Now, following the balanced equation we know that 3 mol of Ba will be produced from 3 mol of BaCl2. Since that means they combine in a 1 to 1 ratio, we know we need to have 0.0309 moles of BaCl2
Step 4: Convert moles BaCl2 to grams BaCl2
0.0309 moles BaCl2 x 208.23 g BaCl2 /mol BaCl2 = 6.60 g BaCl2