 Welcome to the learning activity, the limiting reagent in chemical reactions. The limiting reagent of any chemical reaction is defined as the reactant that is entirely consumed when the reaction goes to completion. Consider making cars. If you add 100 car bodies and 300 tires, how many cars can you make given the equation 1 car body plus 4 tires is equal to 1 car? The answer is 75 cars. Although you have 100 car bodies, you will run out of tires when you complete the 75th car. Here's a chemical example. How much aluminum hydroxide will be obtained by reaction of 13.4 grams of aluminum chloride with 10 grams of sodium hydroxide? Aluminum chloride plus sodium hydroxide is equal to aluminum hydroxide plus sodium chloride. Step 1. Calculate the number of moles of product that each reactant could make. Watch below as the equation is filled out. Step 2. Determine which is the limiting reagent. Although 0.1 moles of aluminum hydroxide can be made from 13.4 grams of aluminum chloride, only 0.0833 moles of aluminum hydroxide can be produced from 10 grams of sodium hydroxide. Sodium hydroxide is the limiting reagent. The limiting reagent is the reagent that gives the smallest quantity of product. Step 3. Determine the weight of the product. Watch below as the equation is filled out. In a reaction where the quantity of one reactant limits the quantity of product formed, the other reactant is in excess. In this case, the excess reagent is aluminum chloride. Watch below as the equation is filled out. In the reaction, sodium plus chlorine is equal to sodium chloride. If 0.1 mole of sodium and 0.1 mole of chlorine are present, which is the limiting reagent? Sodium is the limiting reagent. You can make 0.2 mole of sodium chloride using 0.1 mole of chlorine, but only 0.1 mole of sodium chloride using 0.1 mole of sodium. In the reaction, lithium plus oxygen is equal to lithium oxide. If 0.15 mole of lithium and 0.2 mole of oxygen gas are present, which is the limiting reagent? Lithium is the limiting reagent. You can make 0.4 mole of lithium oxide using 0.2 mole of oxygen, but only 0.075 mole using 0.15 mole of lithium. In the reaction, sodium plus chloride is equal to sodium chloride. If 0.7 moles of sodium and 0.4 moles of chlorine are present, how many moles of sodium chloride can you make? The answer is 0.70. Although you could make 0.80 mole of sodium chloride from 0.4 mole of chlorine, you can only make 0.7 mole of sodium chloride from 0.7 mole of sodium. Sodium is the limiting reagent. Congratulations! You have completed this activity, the limiting reagent in chemical reactions.