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STOICHIOMETRY

- Mole-Mole
- Mole-Mass
- Mass-Mass

STOICHIOMETRY

- the study of the quantitative aspects of chemical reactions.

reactant

Moles

product

STOICHIOMETRY CALCULATIONSStoichiometric

factor

Coef. Want

Coef. given

Mole -Mole Problems

- Moles of the
- Given Substance

Moles of the Unknown Substance

Conversion Factor:

Coefficients from the balanced equation

Example Problem

- 2HCl + Fe = FeCl2 + H2

How many mole of HCl are need to react with 6 mole of Fe?

2HCl

1 Fe

6 molFeX

= 12 mol HCl

Mole -Mass Problems (2 step)

- Moles of the
- Given Substance

¸

Mass of the given Substance

X

Conversion Factor:

Molar mass of the given

product

Mass

reactant

Moles

reactant

Moles

product

STOICHIOMETRY CALCULATIONSMolar mass

Unknown

Molar mass

given

Stoichiometric

factor

Example Problem

- 2HCl + Fe = FeCl2 + H2

How many grams of HCl are need to react with 6 mole of Fe?

2HCl

1 Fe

6 molFeX

= 12 mol HCl

36 g HCl

1 mol

= 432g

12 mol HCl X

Mass -Mass Problems (3 step)

- Mass of the
- Given Substance

Mass of

the Unknown Substance

Conversion Factors:Molar mass of each, and

Coefficients from the balanced equation

product

Mass

reactant

Moles

reactant

Moles

product

STOICHIOMETRY CALCULATIONSMolar mass

Unknown

Molar mass

given

Stoichiometric

factor

= 1 molFe

How many grams of HCl are need to react with 56 g of Fe?

- 2HCl + Fe = FeCl2 + H2

1mol

56 g Fe

56 g of Fe X

2HCl

1 Fe

= 2 mol HCl

1 molFeX

36 g HCl

1 mol

= 72g HCl

2 mol HCl X

PROBLEM: If 454 g of NH4NO3 decomposes, how much N2O and H2O are formed? What is the theoretical yield of products?

STEP 1

Write the balanced chemical equation

NH4NO3 ---> N2O + 2 H2O

454 g of NH4NO3 --> N2O + 2 H2O

STEP 2 Convert mass reactant (454 g) --> moles

STEP 3 Convert moles reactant (5.68 mol) --> moles product

STEP 3 Convert moles reactant --> moles product

Relate moles NH4NO3 to moles product expected.

1 mol NH4NO3 --> 2 mol H2O

Express this relation as the STOICHIOMETRIC

FACTOR.

454 g of NH4NO3 --> N2O + 2 H2O

STEP 3 Convert moles reactant (5.68 mol) --> moles product

= 11.4 mol H2O produced

454 g of NH4NO3 --> N2O + 2 H2O

STEP 4 Convert moles product (11.4 mol) --> mass product

Called the THEORETICAL YIELD

ALWAYS FOLLOW THESE STEPS IN SOLVING STOICHIOMETRY PROBLEMS!

454 g of NH4NO3 --> N2O + 2 H2O

STEP 5 How much N2O is formed?

Total mass of reactants =

total mass of products

454 g NH4NO3 = ___ g N2O + 204 g H2O

mass of N2O = 250. g

454 g of NH4NO3 --> N2O + 2 H2O

STEP 6 Calculate the percent yield

If you isolated only 131 g of N2O, what is the percent yield?

This compares the theoretical (250. g) and actual (131 g) yields.

454 g of NH4NO3 --> N2O + 2 H2O

STEP 6 Calculate the percent yield

PROBLEM: Using 5.00 g of H2O2, what mass of O2 and of H2O can be obtained?

2 H2O2(liq) ---> 2 H2O(g) + O2(g)

Reaction is catalyzed by MnO2

Step 1: moles of H2O2

Step 2: use STOICHIOMETRIC FACTOR to calculate moles of O2

Step 3: mass of O2

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