Question

The theoretical yield of a reaction is the amount of product obtained if the limiting reactant is completely converted to product.

Consider the reaction:
P4(s) + 6 Cl2(g) → 4 PCl3(l)

If 19.47 g P4 is mixed with 6.85 g Cl2, calculate the theoretical yield (g) of PCl3 produced by the reaction.

Answer 1

mols P4 = grams/molar mass = ?
mols Cl2 = grams/molar mass = ?

Using the coefficients in the balanced equation, convert mols P4 to mols PCl3.
Do the same and convert mols Cl2 to mols PCl3.
It is likely that the two values for mols PCl3 sill not agree which means one of them is not right: the correct value in limiting reagent (LR) is ALWAYS the smaller value and the reagent responsible for the value is the LR.

Using the smaller value, convert to grams PCl3.
g PCl3 = mols PCl3 x molar mass PCl3. This number grams will be the theoretical yield.