Excess and Limiting Reactant Percent Yield

This is going to be a difficult chapter so let's break it down. Today's we'll just learn the excess and limiting reactant and the next day would be percent yield.


Excess Quantity: With a balanced equation, we can tell what will happen in the chemical reaction. Except in some cases some reactants may need more or less of one reactant depending the chemical equation if they don't come together.

Excess Quantity in Chemical Reactions: Calculate the amount of products that are being formed and one              reactant would be an excess and one would be a limiting.

Do you get the picture?

No? It's fine!

First let's look at an analogy:

You're working for McDonald's. 

You have 10 hamburger buns and 5 hamburger patties. 

How many hamburgers can you make?

You'll be able to make 5 hamburgers but what was left over?

Solving the puzzle:

There would be 5 hamburger buns in 5 hamburger patty.

Therefore, the beef patty is known as the limiting ingredient since it limits how many burgers can be made.

Got it? Okay, now let's try some chemistry related examples!

Ex. I20.0 g of hydrogen gas react with 100.0 g of oxygen, which reactants is present in excess and by how many grams?

Step 1: Write a balanced equation.

2H2(g) + 1O2 (g) ---->  2H2O(l) 

Step 2: Find which reactants is excess calculate how many grams of H2 would be required to react with 100.0 g of O2 (g). 

100 g O2 x 1 mol O2  x 2 mol H2 x 2.0 g H2

                   16 g O2      1 mol O2    1 mol H2

= 25.0 grams of H2

Step 3: To calculate how much the excess is leftover we must convert O2 ---> H2 to see how much H2 would need to react with O2.

120.0 g H2 x 1 mol H2 x 1 mol O2 x 16.O g O2

                      2 g H2        2 mol H2     1 mol O2       

= 480 grams of O2     

More examples: 

1.2Al + 6HCl →2AlCl3+ 3H2If 25 g of aluminum was added to 90 g of HCl, what mass of H2will be produced (try this two ways –with a chart & using the shortcut)?

2.N2+ 3H2→2NH3: If you have 20 g of N2and 5.0 g of H2, which is the limiting reagent?

3.What mass of aluminum oxide is formed when 10.0 g of Al is burned in 20.0 g of O2?4.When C3H8burns in oxygen, CO2and H2O are produced. If 15.0 g of C3H8reacts with 60.0 g of O2, how much CO2is produced?

Did you say you wanted to learn more about excess and limiting reactants? Well you've scrolled to the right place! Watch this video to learn more!