if you mixed 100 grams of Magnesium nitrite with 100 grams of Lithium Phosphide and made magnesium phosphide and lithium nitrite how many grams of each product would you make and how many grams of each reactant would be left over at the end?

Answer 1

This is a limiting reagent (LR) problem and you know that because amounts are given for both reactants.

3Mg(NO2)2 + 2Li3PO4 ==> Mg3(PO4)2 + 6LiNO2

mols Mg(NO2)2 = grams/molar mass = ?
mols Li3PO4 = grams/molar mass = ?

Using the coefficients in the balanced equation, convert mols Mg(NO2)2 to mols Mg3(PO4)2.
Do the same and convert mols Li3PO4 to mols Mg3(PO4)2.
It is likely that these two values for mols Mg3(PO4)2 will not agree; the correct value in LR problems is ALWAYS the smaller number and the reagent responsible for this is the LR. This identifies the LR. Remember this for later. That will be called the LR and the other reagent will be called OR (for other reagent).
Convert to grams by g = mols x molar mass.
Using the LR, convert, with the coefficients, mols LR to mols LiNO2. Then convert to grams by mols x molar mass. This takes care of all but the lat part of the problem; i.e., how much is left of each one.

How much is left of the LR. Answer is none since all of it is used up.
How to find mols OR used.
Using the coefficients in the balanced equation, convert mols of the LR used to mols OR used. Subtract initial mols - mols used = mols remaining.
Then convert to grams. g OR remaining = mols OR x molar mass OR.
Post all of your work if you get stuck.