how do I write out this problem? How many grams of lithium metal would be produced if 0.500 grams of magnesium was added to a solution of lithium chloride
I don't know how you write it out. The reaction will not occur; i.e., magnesium metal will NOT displace Li from a salt such as LiCl.
I would do this if I had to write it out.
Mg(s) + LiCl(aq) ==> no reaction.