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Limiting reagent

Content objective:

What are we learning and why are we learning this? Content, procedures, or skills.

Vocabulary objective

Tier II: High frequency words used across content areas. Key to understanding directions & relationships, and for making inferences.

Tier III: Low frequency, domain specific terms.

Building on what we already know

Make connections to prior knowledge. This is where we build from.


We want to bake cookies! Here’s the recipe: 2 cups of flour, 1 cup chocolate chips, 2 eggs, and water

Yields: 12 cookies. How many cookies can we make? We’re given 100 cups of flour, 100 cups of chocolate chips, an unlimited amount of water, and 4 eggs. But we can only bake 24 cookies. Why?

chocolate chip cookies

We run out of eggs after making the 24 cookies. So we say that the eggs are our limiting ingredient.  In chemistry, we use the word reagent instead of ingredient, but it means the same thing. Eggs are our limiting reagent.


What about cheese sandwiches? We have 6 slices of whole-grain bread (*), and 2 slices of thickly sliced Swiss cheese. Our recipe calls for 1 slice/sandwich. How many sandwiches can we make? Just 2. Even though we have more bread left over, cheese is our limiting reagent.

(*) Don’t even think about eating that bleached, refined white bread nonsense.

Limiting reagent cheese sandwiches


How about a more sophisticated sandwich?


The same goes for making hamburgers (*) Use 1 slice of cheese, 2 leaves lettuce, 1 bun, and 1 burger per person. How many burgers can we make from the below ingredients?

(*) Chipotle veggie burgers are even better for you! Just sayin’ 🙂

How many hamburgers can be made? What is the limiting reagent (ingredient)?


How do limiting reagents work for chemistry?

In exactly the same way!

Reactants:  N2 (nitrogen gas) and H2 (hydrogen gas)

Products:   NH3 (ammonia)  +  any possible left overs

So what happens here?

All N2 is consumed

2 molecules ammonia produced

Limiting reagent? the N2

Leftovers? H2 gas – we say that H2 is present in excess

ammonia stoichiometry

Prentice Hall


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