A student carried out the reaction shown by reacting 10.0g P4 with excess Cl2 and obtained 35.0g of PCl3.

P4 + 6Cl2----->4PCl3

a. What is the theoretical yield of PCl3?

See the problem I worked for you above. That amount you get for the product, in grams, is called theoretical yield. Many problems like this have a second problem to go with it in which they ask for the percent yield That is %yield = (g actual yield/g theoretical yield)*100 = ?