StoichiometryStoichiometry

Chapter 9Chapter 9

Limiting reagentsLimiting reagents

In Stoichiometry: We work in In Stoichiometry: We work in moles.moles.

We cannot calculate grams of We cannot calculate grams of product from grams of reactantproduct from grams of reactant

Step 1: Grams of reactant to moles of Step 1: Grams of reactant to moles of reactantreactant

Step 2: Moles of reactant to moles of Step 2: Moles of reactant to moles of productproduct

Step 3: Moles of product to grams of Step 3: Moles of product to grams of productproduct

ReviewReview Converting mass to Converting mass to

moles: divide grams moles: divide grams by molar massby molar mass

Converting moles to Converting moles to mass: multiply moles mass: multiply moles by molar massby molar mass

Converting moles to Converting moles to particles: multiply particles: multiply moles by 6.02 x 10moles by 6.02 x 102323

Can you go from Can you go from mass to particles?mass to particles?

Limiting ReagentsLimiting Reagents

Limiting Reagents: a videoLimiting Reagents: a video

http://wps.prenhall.com/wps/media/objectshttp://wps.prenhall.com/wps/media/objects/439/449969/Media_Portfolio/Chapter_11//439/449969/Media_Portfolio/Chapter_11/Limiting_Reagent.MOVLimiting_Reagent.MOV

Theoretical YieldTheoretical Yield This is the amount of product expected in This is the amount of product expected in

a perfect world with the amount of reactant a perfect world with the amount of reactant given.given.

In Limiting reagent problems, you find the In Limiting reagent problems, you find the amount each reactant would produce with amount each reactant would produce with no other constraints. That is two or more no other constraints. That is two or more calculations depending on the number of calculations depending on the number of reactants.reactants.

The reactant that forms the least amount The reactant that forms the least amount of product in its theoretical yield is the of product in its theoretical yield is the limiting reagent.limiting reagent.

How to do these problems:How to do these problems:First write a balanced chemical First write a balanced chemical

equation.equation.Find the molar mass of each “player” Find the molar mass of each “player”

be it product or reactant. be it product or reactant. (coefficients are not used to (coefficients are not used to calculate molar mass)calculate molar mass)

Convert the mass of each reactant Convert the mass of each reactant given to moles. Grams divided by given to moles. Grams divided by grams/mol.grams/mol.

How to continued:How to continued:

Find the molar ratio to convert moles of Find the molar ratio to convert moles of reactant to moles of product. (This is reactant to moles of product. (This is where you use coefficients)where you use coefficients)

Convert moles of product to grams of Convert moles of product to grams of product.product.

If this is a limiting reagent problem, repeat If this is a limiting reagent problem, repeat for the other reactant and compare results.for the other reactant and compare results.

If you can add, subtract, divide, and If you can add, subtract, divide, and multiply, you can do this!!multiply, you can do this!!

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