Nearly everything we use is manufactured from chemicals.›Soaps, shampoos, conditioners, cd’s, cosmetics, medications, and clothes.

For a manufacturer to make a profit the cost of making any of these items can’t be more than the money paid for them.

Chemical processes carried out in industry must be economical, this is where balanced equations help.

Equations are a chemist’s recipe.◦They tell chemists what amounts of reactants to mix and what amounts of products to expect.

When you know the quantity of one substance in a reaction, you can calculate the quantity of any other substance consumed or created in the rxn.◦Quantity meaning the amount of a substance in grams, liters, molecules, or moles.

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The calculation of quantities in chemical reactions is called stoichiometry.

Assume that the major components of the bike are the frame (F), the seat (S), the wheels (W), the handlebars (H), and the pedals (P).

The finished bike has a “formula” of FSW2HP2.

The balanced equation for the production of 1 bike is.F +S+2W+H+2P FSW2HP2

Now in a 5 day workweek, A company is scheduled to make 640 bikes. How many wheels should be in the plant on Monday morning to make these bikes?

What do we know?◦ Number of bikes = 640 bikes

◦ 1 FSW2HP2=2W (balanced eqn) What is unknown?

◦ # of wheels = ? wheels

• F +S+2W+H+2P FSW2HP2

The connection between wheels and bikes is 2 wheels per bike. We can use this information as a conversion factor to do the calculation.

640 FSW2HP2

1 FSW2HP2

2 W= 1280

wheels

• We can make the same kinds of connections from a chemical rxn eqn.N2(g) + 3H2(g) 2NH3(g)

• The key is the “coefficient ratio”.

◦ The coefficients of the balanced chemical equation indicate the numbers of moles of reactants and products in a chemical rxn.

1 mole of N2 reacts with 3 moles of H2 to produce 2 moles of NH3.◦N2 and H2 will always react to form

ammonia in this 1:3:2 ratio of moles.

So if you started with 10 moles of N2 it would take 30 moles of H2 and would produce 20 moles of NH3

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

Using the coefficients, from the balanced equation to make connections between reactants and products, is the most important information that a rxn equation provides.

› Using this information, you can calculate the amounts of the reactants involved and the amount of product you might expect.

› Any calculation done with the next process is a theoretical number, the real world isn’t always perfect.

The following rxn shows the synthesis of aluminum oxide.

3O2(g) + 4Al(s) 2Al2O3(s)

• If you only had 1.8 mols of Al how much product could you make?

Given: 1.8 moles of Al

Uknown: ____ moles of Al2O3

3O2(g) + 4Al(s) 2Al2O3(s)

Solve for the unknown:

1.8 mol Al4 mol Al

2 mol Al2O3 = 0.90mol Al2O3

3O2(g) + 4Al(s) 2Al2O3(s)

Mole Ratio

The following rxn shows the synthesis of aluminum oxide.

3O2(g) + 4Al(s) 2Al2O3(s)

• If you wanted to produce 24 mols of product how many mols of each reactant would you need?Given: 24 moles of Al2O3

Uknown: ____ moles of Al ____ moles of O2

Solve for the unknowns:

24 mol Al2O32 mol Al2O3

4 mol Al= 48 mol Al

3O2(g) + 4Al(s) 2Al2O3(s)

24 mol Al2O32 mol Al2O3

3 mol O2 = 36 mol O2

1. How many moles of potassium chlorate, KClO3 are needed to produce 5 mol O2 given the following BALANCED EQUATION?

2KClO3 2 KCl + 3O2

2. Sodium metal reacts with chlorine gas to produce sodium chloride. Write a balanced chemical equation. If 3.75 mol Na react with enough chlorine gas, how much sodium chloride is produced?

No lab balance measures moles directly, generally mass is the unit of choice.

From the mass of 1 reactant or product, the mass of any other reactant or product in a given chemical equation can be calculated, provided you have a balanced rxn equation.

As in mole-mole calcs, the unknown can be either a reactant or a product.

Acetylene gas (C2H2) is produced by adding water to calcium carbide

(CaC2).

How many grams of C2H2 are produced by adding water to 5.00

g CaC2?

CaC2 + 2H2O C2H2 + Ca(OH)2

What do we know?◦Given mass = 5.0 g CaC2

◦Mole ratio: 1 mol CaC2 = 1 mol C2H2 (from balanced equation)

◦Molar Mass (MM) of CaC2 = 64.0 g/mol CaC2

◦Molar Mass of C2H2 = 26.0g/mol C2H2 What are we asked for?

◦grams of C2H2 produced

CaC2 + 2H2O C2H2 + Ca(OH)2

mass A moles A moles B mass B

What mass of copper is required to react with 4.00g of silver nitrate ?

Cu + 2AgNO3 2Ag + Cu(NO3)2

How many grams of O2 are produced when a sample of 29.2 g of H2O is decomposed by electrolysis according to this balanced

equation:2H2O 2H2 + O2

Aspirin can be made from a chemical rxn between the reactants salicylic acid and acetic anhydride. The products of the rxn are acetyl-salicylic acid (aspirin) and acetic acid (vinegar). Our factory makes 125,000 100-count bottles of Bayer Aspirin/day. Each bottle contains 100 tablets, and each tablet contains 325mg of aspirin. How much in kgs + 10% for production problems, of each reactant must we have in order to meet production?

C7H6O3 + C4H6O3 C9H8O4 + HC2H3O2

Salicylic acid

Acetic anhydride aspirin vinegar

What are we asked for?◦ Mass of salicylic acid in kgs + 10%◦ Mass of acetic anhydride in kgs + 10%

What do we know?◦Make 125,000 aspirin bottles/day◦100 aspirin/bottle◦325 mg aspirin/tablet◦Mole ratio of aspirin to salicylic acid (1:1)

and acetic anhydride (1:1)◦MM aspirin = 180.11g/mol◦MM C7H6O3 = 138.10g/mol◦MM C4H6O3 = 102.06g / mol

C7H6O3 + C4H6O3 C9H8O4 + HC2H3O2

125,000 bottles

1 bottle

100 tablets

1 tablet

325mg asp.

1000 mg

1 g

How many grams of aspirin do I need to produce?

C7H6O3 + C4H6O3 C9H8O4 + HC2H3O2

In a chemical reaction, an insufficient quantity of any of the reactants will limit the amount of product that forms.

Limiting reactant (reagent): reactant that determines the amount of product that can be formed in the reaction.

Excess reactant (reagent): reactant that is not completely used up in a reaction.

Theoretical yield: The maximum quantity of product that a reaction could theoretically make (calculated based upon limiting reactant).

Calculate how much product (Cu2S) each amount of reactant produces respectively.