StoichiometryStoichiometryStoichiometry (  /ˌstɔɪkiˈɒmɨtri/) is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions.

•used to find quantities such as the amount of products (in mass, moles, volume, etc.) that can be produced with given reactants and percent yield

•founded on the law of conservation of mass: the mass of the reactants equals the mass of the products.

=-from Wikipedia

Relationships shown in Chemical Equations

Balanced Chemical Equation

4 Fe (s) + 3 O2 (g) 2 Fe2O3 (s)

Word equation Iron (III) Oxygen Iron (III) Oxide

Particle Model

Atom/Molecule Relationship

4 atoms Fe

3 molecules O2

2 Formula Units Fe2O3

Mole to mole Relationship

4 mol Fe 3 mol O2 2 mol Fe2O3

Mass relationship 223.4 g Fe

96.00 g O2 319.4 g Fe2O3

Reactant-Product Relationship

319.4 g reactants 319.4 g products.

Relationships shown in Chemical Equations

Identify ALL of the molar ratios in the equation.

4 P + 5 O2 2 P2O5

What is the molar mass of each substance?

Relationships shown in Chemical Equations

6)  Chlorine is used by textile manufacturers to bleach cloth. Excess chlorine is destroyed by its reaction with sodium thiosulfate, Na2S2O3:

Na2S2O3(aq) + 4Cl2(g) + 5H2O(aq) 2NaHSO4(aq) + 8HCl(aq) 

 a. How many moles of Na2S2O3 are needed to react with

0.12mol of Cl2?

  b. How many moles of HCl can form from 0.12mol of Cl2?

Stoichiometry

Limiting Reactants

A cake recipe calls for – 2 cups of water – 4 cups of flour – 8 squares of chocolate – 4 cups of sugar – 8 oz of butter – 4 eggs

According to Model 1, how much of each ingredient is necessary to make a cake?

If you follow the recipe, using only the ingredients on hand in the model, how much of each ingredient will be left over after you have baked the cake?

2 c water

4 cups of flour

8 squares of chocolate

4 cups of sugar

8 oz butte

r

4 eggs

lots 1 cup 4 squares

none 8 oz. 2 eggs

Which of the ingredients on hand were in excess for the recipe?

Which of the ingredients on hand were consumed completely in making the cake?

Which of the ingredients limit or prevent you from making a second cake?

What would be a good definition for the term

limiting ingredient?

lots 1 cup 4 squares

none 8 oz. 2 eggs

A cake recipe calls for

–2 cups of water

–4 cups of flour

–8 squares of chocolate

–4 cups of sugar

–8 oz of butter

–4 eggs

Limiting Reactant

You have 10 bolts, 15 nuts, and 15 washers. You assemble a nut/bolt/washer set using the following recipe or equation. 2 washers + 1 bolt + 1 nut = 1 set

(a) How many sets can you assemble from your supply?

(b) Which is the limiting component?

How can you identify the limiting component in some manufacturing process?

Limiting Reactant

How could we write a chemical equation for this example?

Limiting Reactant

• If have 365 cars and 1208 tires, how many cars can I make?

Check problem #1Ammonia (NH3) is one of the most common

chemicals produced in the United States. It is used to make fertilizer and other products. Ammonia is produced by the following chemical reaction.

N2(g) 3H2(g) 2NH3(g)

 a. If you have 1.00 x 103 g of N2 and 2.50 x 103 g of

H2, which is the limiting reactant in the reaction?

b. How many grams of ammonia can be produced from the amount of limiting reactant available?

c. Calculate the mass of excess reactant that remains after the reaction is complete.