Stoichiometry
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Stoichiometry. Chapter 9. Stoichiometry. In this chapter, we will revisit the mole concept and use it to relate quantities of reactants & products. Stoichiometry. What is stoichiometry? Outside world connections – cooking, manufacturing, etc. Interpreting balanced chemical equations.

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Stoichiometry

Stoichiometry

Chapter 9


Stoichiometry1

Stoichiometry

  • In this chapter, we will revisit the mole concept and use it to relate quantities of reactants & products.


Stoichiometry2

Stoichiometry

What is stoichiometry?

  • Outside world connections – cooking, manufacturing, etc.

  • Interpreting balanced chemical equations


Stoichiometry3

Stoichiometry

What is stoichiometry?

  • Chemical equation consists of reactants & products, coefficients are there to give # of particles involved (moles, molecules, formula units, atoms, etc.)

    • Will later use coefficients from balanced equations to find actual amounts of substances (mass, volume, etc.)


Stoichiometry example

Stoichiometry Example

French Toast

  • 3 eggs, slightly beaten

  • 1 c milk

  • ½ tsp salt

  • 6 slices of bread

  • 2 Tbs sugar


Stoichiometry example1

Stoichiometry Example

French Toast

  • The recipe makes 6 slices of French Toast. How would you make 12 slices?

  • What is the ratio of eggs to bread? Did it change when the recipe was increased to make more servings?

  • What would happen if you tried to make the recipe with only 1 egg?


Stoichiometry example2

Stoichiometry Example

Following a recipe is a lot like performing a chemical reaction. You have to have the right reactants and enough of each one or things will not turn out as planned.


Stoichiometry4

Stoichiometry…

Ratios are very important in balanced chemical equations.

  • What is the ratio of H2 to O2 in the following equation?

    • 2 H2 + O2 2 H2O

  • Would the ratio change if more water was produced? Why?


Stoich problems

Stoich Problems

How do I use stoichiometry?

  • Follow the process for solving problems: qty of given  moles of given  moles of unknown  qty of unknown


Beginning stoich

Beginning Stoich

Mole-mole problems

  • Converting from moles of one substance to moles of another substance requires a mole ratio from the balanced chemical equation


Beginning stoich1

Beginning Stoich

Mole-mole problems

Ex 1:

  • A pink paint is produced by using 3 L of white & 1 L of red

    • The paint ratio is ______

    • If we only want 2 L of pink paint what do we need?

      • Mix ___ L white & ___ L red


Beginning stoich2

Beginning Stoich

Mole-mole problems

Ex 2:

  • NH4NO3 N2O + 2 H2O

  • Suppose we wanted to know the number of moles of product created by 2.25 moles ammonium nitrate


Beginning stoich3

Beginning Stoich

Mole-mole problems

Ex 3:

  • 2 HCl + Zn  ZnCl2 + H2

  • How many moles HCl needed to react with 5.70 moles Zn?


Beginning stoich4

Beginning Stoich

Mole-mole problems

Ex 4:

  • N2O5 + H2O  2 HNO3

  • How many moles HNO3 produced from 0.51 moles N2O5?


Beginning stoich5

Beginning Stoich

Mole-mole problems

Ex 5:

  • Pb + 2 HCl  PbCl2 + H2

  • How many moles HCl needed to react with 0.36 moles Pb?


Beginning stoich6

Beginning Stoich

Verifying the law of conservation of matter

Balanced eqs “obey” the law:

  • 2 H2 + O2 2 H2O

  • 2 moles H2(@ 2.016 g/mole)= g

  • 1 mole O2(@ 32.00 g/mole)= g

  • 2 moles water(@ 18.016 g/mole) = g


Stoich problems1

Stoich Problems

4 types of problems:

1) Mass-mass – given mass of one substance & asked to find mass of another

  • Process: (g of given) * (1 mole/molar mass of given) * (ratio of wanted to given) * (molar mass of wanted/1 mole)


Stoich problems2

Stoich Problems

4 types of problems:

1) Mass-mass

Example 1: How many grams of AgCl can be produced when 17.0 g AgNO3 reacts with NaCl?


Stoich problems3

Stoich Problems

4 types of problems:

1) Mass-mass

Example 2: How many grams of Cu2S can be produced from 9.90 g of CuCl reacting with H2S?


Stoich problems4

Stoich Problems

4 types of problems:

2) Mass-volume - given mass of one substance & asked to find volume of another

  • Process: (g of given) * (1 mole/molar mass of given) * (ratio of wanted to given) * (molar volume/1 mole)


Stoich problems5

Stoich Problems

4 types of problems:

2) Mass-volume

Example 1: What volume of H2 can be produced (at STP) when 6.54 g Zn reacts with HCl?


Stoich problems6

Stoich Problems

4 types of problems:

2) Mass-volume

Example 2: What volume of ammonia can be produced from 14.01 g N2 reacting with H2?


Stoich problems7

Stoich Problems

4 types of problems:

3) Volume-mass - given volume of one substance & asked to find mass of another

  • Process: (volume of given) * (1 mole/molar volume of given) * (ratio of wanted to given) * (mass/1 mole)


Stoich problems8

Stoich Problems

4 types of problems:

3) Volume-mass -

Example 1: How many grams of NaCl can be produced by reacting 112 mL Cl2 (@ STP) w/ Na?


Stoich problems9

Stoich Problems

4 types of problems:

3) Volume-mass -

Example 2: Bromine reacts with 5600 mL hydrogen to give what mass of HBr at STP?


Stoich problems10

Stoich Problems

4 types of problems:

4) Volume-volume - given volume of one substance & asked to find volume of another

  • Process: (volume of given) * (1 mole/molar volume of given) * (ratio of wanted to given) * (molar volume/1 mole)


Stoich problems11

Stoich Problems

4 types of problems:

4) Volume-volume -

Example 1: How many L of O2 are needed to burn 1.00 L of methane (@ STP)?


Stoich problems12

Stoich Problems

4 types of problems:

4) Volume-volume -

Example 2: What volume of Br2 is produced if 75.2 L of Cl2 react with HBr?


Limiting reactant

Limiting Reactant

Limiting reactant – substance that determines how much product may be formed (or how much reactant was available)


Limiting reactant1

Limiting Reactant

Limiting reactant –

  • Identifying –

    • Determine possible amount of desired substance (need to do 2 dimensional analysis problems)

      • The limiting reactant is the substance that results in the least amount of desired substance


Limiting reactant2

Limiting Reactant

Limiting reactant Problems

Ex. 12 Fe + 3 S  Fe2S3

  • Given 111.7 g Fe & 160.35 g S, how many grams of product can be formed?


Limiting reactant3

Limiting Reactant

Limiting reactant Problems

Ex. 2Cu + 2 AgNO3 Cu(NO3)2 + 2 Ag

  • Given 3.5 g copper & 6.0 grams silver nitrate, how much silver can be formed?


Limiting reactant4

Limiting Reactant

Limiting reactant Problems

Ex. 3Zn + S  ZnS

  • Given 3.5 g each reactant, how much product formed?


Percent yield

Percent Yield

  • how much product is formed compared with expected results

    % yield = (actual amount/expected amount) x 100

    (units are in terms of %)


Percent yield1

Percent Yield

Ex. 1) You combined 4.3 liters of Cl2 with some Na. You were able to recover 15.9 g of NaCl. What was the percent yield?

  • 2 Na + Cl2 2 NaCl


Percent yield2

Percent Yield

Ex. 2) 5.00 grams of Cu mixed with excess AgNO3. This gave 15.2 g of Ag. What was the percent yield?

  • Cu + 2 AgNO3 Cu(NO3)2 + 2 Ag


Percent yield3

Percent Yield

Ex 3) If 320. grams of octane are burned in oxygen and 392 grams of water are produced. What was the percent yield?

  • 2 C8H18 + 25 O2 16 CO2 + 18 H2O


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