Let's say you want to make some pizzas. Your recipe for pizza requires one crust, eight ounces of pizza sauce, and four cups of cheese. You have five crusts, 24 ounces of pizza sauce, and 16 cups of cheese. How many pizzas can you make from these ingredients? If you said three pizzas, you intuitively understand the idea of limiting reagent. We can solve this problem using dimensional analysis by converting our amounts of each reactant into the amount of product. We have five pizza crusts and each pizza requires one pizza crust, so we have enough crust to make five pizzas. We have 24 ounces of pizza sauce and each pizza requires 8 ounces of sauce, so we have enough sauce for three pizzas. And we have 16 cups of cheese and each pizza requires 4 cups of cheese, so we have enough cheese for four pizzas. Since we can create the fewest number of pizzas from the pizza sauce, this ingredient limits the amount of pizza we can theoretically make. In the previous problem, pizza sauce was our limiting reactant or limiting reagent. The limiting reagent produces the least amount of product, thus limiting how much product can be produced. Pizza crusts and pizza sauce were our excess reagents or excess reactants. Excess reactants are all the reactants that have some left over after reacting completely with the limiting reagent. In our problem, three pizzas was our theoretical yield, which is the amount of product we can produce based on our limiting reagent. We can calculate how much excess reactant is leftover based on our theoretical yield. We calculated previously that we should be able to produce three pizzas based on our limiting reagent, pizza sauce. So we can calculate how much of our excess reagents are required to produce three pizzas. We'll need three crusts to produce three pizzas. We started with five crusts, and we'll use three crusts to produce those three pizzas, so we should have two crusts left over. We'll also need 12 cups of cheese to produce three pizzas. We started with 16 cups of cheese, and we used 12 cups of cheese to produce our three pizzas, so we should have 4 cups of cheese left over. When you actually run an experiment, you may get a different amount of product than you calculated you should be able to produce. The amount of product you actually produce when you perform an experiment is called the actual yield. The percent yield is the actual yield divided by the theoretical yield, times 100%. So let's say when you try to create your pizza from the recipe, you actually produce two pizzas. Let's calculate the percent yield. Our equation for percent yield is actual yield divided by theoretical yield, times 100%. We calculated the theoretical yield based on our limiting reagent: our theoretical yield is three pizzas. We're given the actual yield in the problem, which is two pizzas. Plugging these into our equation and completing the calculation, we get 66.7%. This is our percent yield.