How to balance equations when you are only given half of the equation?

Ba and Fe tend to be cations (like to lose electrons to become postive ions). Cl and SO4 tend to be anions (negatively charged ions). Positive ions like to interact with negative ions, so it should make sense that BaSO4 is formed and FeCl3 is formed as the product. Fe can be 2+ or 3+, but SO4 is always with a charge of -2. You can see from the reactant, Fe2(SO4)3 that 3 of them "interact" with 2 Fe, giving a total of -6 charge for SO4^-2. Since there is no charge on either of the reactants, Fe has to be +3 charge (2 *3 = 6) to give a neutral Fe2(SO4)3. Since this is NOT an electron transfer reaction, Fe will remain +3 when it is bonded to FeCl3 and Cl is nearly always -1 charge, so three of them will cancel out the Fe3+ charge. Hope that helps