Corban E. answered 05/08/21
AP Chemistry Tutor and Former Teacher (Gen Chem, IB, O-Level, A-Level)
mol to mol with coefficients
0.51 mol Li3PO4 (3 mol Li2CO3 / 2 mol Li3PO4)=0.765 mol Li2CO3
mol to g with molar mass. Note that coefficients don't affect molar mass.
0.765 mol Li2CO3 (73.888 g Li2CO3 / 1 mol Li2CO3)=56.524=57 g Li2CO3