# How does a limiting reagent affect how much product is formed?

Apr 25, 2014
• The limiting reagent in a reaction is the reactant that runs out first. Once it is completely consumed, the reaction stops.

After the limiting reactant has been used up, any excess reagent will be unable to produce more products.

• Suppose that you are in a car factory. To assemble a car, you need 4 tires and 2 headlights. If you have 20 tires and 14 headlights, how many cars can you make?

With 20 tires, you can produce 5 cars because there are 4 tires to a car. With 14 headlights, you can build 7 cars, because each car needs 2 headlights.

• You can make more cars from the headlights available, but you can make only 5 full cars because of the number of tires available. This makes the tires the limiting reactant in this $r e a c t i o n$.

You can keep building cars until you have used all the tires. Then you have to stop, even though you still have headlights available.

In the same way, a chemical reaction stops when the limiting reactant is used up. After that, you get no more product.

Here is a video which discusses how to calculate limiting reactants.