What is the percent yield for the reaction

PCl3(g) + Cl2(g) --> PCl5(g)

if 119.3 g of PCl5 are formed when 61.3 g of Cl2 react with excess PCl3?

I don't understand how to set this up?

This is a stoichiometry problem. Here is a worked example. Most stoichiometry problems are worked the same way. Copy this and remember the steps. It will save you a lot of time in the future.

http://www.jiskha.com/science/chemistry/stoichiometry.html

I understand how to do the steps. but the wording is different on this problem, that is what I don't understand?

The only difference here is that the problem TELLS you that 119.3 g PCl5 were formed. That is the ACTUAL yield. So use the 61.3 g Cl2 as the starting material and go through the steps in the worked example. The answer you obtain will be the THEORETICAL YIELD (Look down through the problem and that example tells you that, also, in step 4. It also explains how to calculate the percent yield).

percent yield = (actual yield/theoretical yield)*100 =
(119.3/theoretical yield)*100 = ??

To determine the percent yield for a reaction, we need to compare the actual yield (the amount of product actually obtained) to the theoretical yield (the maximum amount of product that can be formed based on stoichiometry).

Let's start by calculating the theoretical yield of PCl5 using the given information:

1. Determine the limiting reactant:
To find the limiting reactant, we compare the given amount of each reactant to their respective coefficients in the balanced equation. In this case, we compare the amount of Cl2 (61.3 g) and PCl3 (not given but assumed to be in excess) to their coefficients in the balanced equation:

PCl3(g) + Cl2(g) -> PCl5(g)
From the balanced equation, we can see that the coefficient of Cl2 is 1, and the coefficient of PCl3 is also 1.
Therefore, the limiting reactant is Cl2.

2. Calculate the number of moles of the limiting reactant:
To determine the number of moles, we use the given mass and the molar mass of Cl2.
The molar mass of Cl2 is 70.906 g/mol.

Number of moles of Cl2 = mass of Cl2 / molar mass of Cl2
Number of moles of Cl2 = 61.3 g / 70.906 g/mol

3. Determine the stoichiometric ratio:
From the balanced equation, we can see that the stoichiometric ratio between Cl2 and PCl5 is 1:1. This means that 1 mole of Cl2 reacts to produce 1 mole of PCl5.

4. Calculate the theoretical yield of PCl5:
Since the stoichiometric ratio is 1:1, the theoretical yield of PCl5 is equal to the number of moles of Cl2 calculated in step 2.

Theoretical yield of PCl5 = Number of moles of Cl2

5. Convert the theoretical yield from moles to grams:
To convert the theoretical yield from moles to grams, we multiply the number of moles by the molar mass of PCl5.
The molar mass of PCl5 is 208.239 g/mol.

Theoretical yield of PCl5 in grams = Theoretical yield of PCl5 in moles * molar mass of PCl5

Now that you have calculated the theoretical yield of PCl5, you can proceed to calculate the percent yield by dividing the actual yield by the theoretical yield and multiplying by 100.

Percent yield = (Actual yield / Theoretical yield) * 100