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.

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.

To calculate the theoretical yield of a reaction, you need to follow these steps:

Step 1: Convert the given masses of reactants to moles.
The molar mass of P4 is 123.9 g/mol. Therefore, the number of moles of P4 is calculated as follows:
moles of P4 = mass of P4 / molar mass of P4
= 19.47 g / 123.9 g/mol
≈ 0.157 mol

The molar mass of Cl2 is 71 g/mol. Therefore, the number of moles of Cl2 is:
moles of Cl2 = mass of Cl2 / molar mass of Cl2
= 6.85 g / 71 g/mol
≈ 0.097 mol

Step 2: Determine the mole ratio between the reactants.
According to the balanced equation:
1 mole of P4 reacts with 6 moles of Cl2 to produce 4 moles of PCl3.
This means the mole ratio between P4 and Cl2 is 1:6.

Step 3: Identify the limiting reactant.
To determine the limiting reactant, you compare the mole ratio from the equation with the actual mole ratio from the given amounts of reactants. In this case, since the mole ratio of P4 to Cl2 is 1:6, and we have 0.157 mol of P4 and 0.097 mol of Cl2, we can see that Cl2 is the limiting reactant since we have less of it.

Step 4: Calculate the theoretical yield.
To calculate the theoretical yield, you need to consider the stoichiometry of the reaction. For every 1 mole of P4, 4 moles of PCl3 are produced.
So, moles of PCl3 = moles of Cl2 × (4 moles of PCl3 / 6 moles of Cl2)
= 0.097 mol × (4 mol/ 6 mol)
≈ 0.065 mol

Finally, to find the mass of PCl3, you multiply the moles of PCl3 by its molar mass.
mass of PCl3 = moles of PCl3 × molar mass of PCl3
= 0.065 mol × 137.3 g/mol
≈ 8.94 g

Therefore, the theoretical yield of PCl3 produced by the reaction is approximately 8.94 grams.