Stoichiometry

What do I get when I have????

What is Stoichiometry?

a branch of chemistry that deals with the quantitative relationships that exist between the reactants and products in chemical reactions.

Stoichiometry can be used to calculate quantities such as the amount of products that can be produced with given reactants and percent yield (the percentage of the given reactant that is made into the product).

In Other words

How much product do I get when I mix certain amounts of Reactants together,

Or, How much do I need to make what I want.

Steps in Stoichmetry

1. Write the Balanced Chemical Equation.

2. Convert the grams given into moles.

3. Multiply by the mole ratio from the Balanced Chemical Equation.

4. Convert the new number of moles to grams.

Why did I have to learn the Mole Equations? The second step in Stoichiometry requires

you to convert from grams to moles (or things to moles)

The fourth step in Stoichiometry requires you to convert from moles to grams (or moles to things)

Railroad Track Stoichiometry

The best way to learn is to do it

So here we go: You have 5 grams of Lead (II) Nitrate mixed with an excess of Sodium Chloride, how many grams of Lead (II) Chloride will you produce?

Step 1, write the balanced equation: Pb(NO3)2+ 2 NaCl PbCl2 + 2 NaNO3

Step 2: Convert grams to moles

Step 3: Multiply by mole ratio

Step 4: Convert back to grams

And the Answer is:

One More time

You have 5 grams of Lead (II) Nitrate mixed with an excess of Sodium Chloride, how many grams of Sodium Nitrate will you produce?

Step 1, write the balanced equation: Pb(NO3)2+ 2 NaCl PbCl2 + 2 NaNO3

Step 2: Convert grams to moles

Step 3: Multiply by mole ratio

Step 4: Multiply by New Molar Mass

And the Answer is:………

Moles instead of grams???

In case of this, you can skip either step 2 or step 4, YEAH!!!!!!!!!!!!

How many moles of Lead (II) Nitrate are needed to produce 6 grams of Sodium Nitrate?

Back to Step 1: Pb(NO3)2+ 2 NaCl PbCl2 + 2 NaNO3

Starting in grams, so

We still need Step 2:

Still have to do Step 3:

Moles to Moles:

Limiting Reagent Problems

Chemical Reactions will continue until one of the Reagents (Reactants) is used up.

Once one of the Reagents is used up, the reaction stops!

It doesn’t matter how much of the other one (Excess) is still left, the reactions STOPS.

Limiting Reactants require TWO complete Stoichiometry Equations One for each Reactant: SAME FOUR STEPS, Two times……….. If 5.00 grams of Lead (II) Nitrate is reacted

with 5.00 grams of Sodium Chloride, what is the Limiting Reactant (Reagent), and how much of the solid product is produced?

Same STEP 1: Pb(NO3)2+ 2 NaCl PbCl2 (s) + 2 NaNO3

It is a gram to gram problem, so…

You still have to do all the steps, but twice. Once for each reactant:

Continuing:

And…….

5.00 g Lead (II) Nitrate makes 4.20 g of Lead (II) Chloride.

5.00 g Sodium Chloride makes 9.81 grams of Lead (II) Chloride.

So, Lead (II) Nitrate is the Limiting Reagent because it makes the least Product.

Sodium Chloride is the Excess Reagent, it makes the most Product.

Only the Least Amount can be made, so only 4.20 g of Lead (II) Chloride is produced.

YOU CAN ONLY MAKE THE …

LEAST AMOUNT OF PRODUCT. A Car can only go as far as the Gasoline lets

it go!!!!!!!!!!!

Percent Yield

Stiochiometry gives us a perfect answer in a perfect world.

In the Real World not every atom reacts. If you run your car out of gas, you can still

smell gasoline in the gas tank, some it still left, but the car won’t run.

Percent Yield Formula

Example

In a chemical reaction between Lead (II) Nitrate and Sodium Chloride the Stoichiometry determined that 4.20 grams should be produced. When the Experiment was actually performed, 3.95 grams was produced. What is the Percent Yield?

% yield = 3.95 g actual X 100 = 94.05 %

4.20 g predicted