Review

§What is the molar mass of the following compounds?§BF3

§68 g/mol§MgO

§40 g/mol§How many grams of 3 moles of H2O?

§54 g H2O§Balance the following: ____ Al + _____ O2 à _____ Al2O3

§4 Al + 3 O2 à 2 Al2O3

STOICHIOMETRIC CALCULATIONS

REMEMBER THIS?

§Calculate the molar mass of the compound CaCl2.§111 g/mol CaCl2

§What is the mass in grams of 2 moles of CaCl2? §222 g CaCl2

§We can convert between moles, particles, and grams, but … this only gives us information about one substance!

§How do we determine how much reactants to use in a chemical reaction? Or how much product will we create?

Stoichiometry! J

WHAT IS STOICHIOMETRY?

§Stoichiometry: the quantitative relationship between reactants and products in a chemical reaction§Based on the mole ratio§What to expect:

ü Molar ratiosüMolar massesüBalancing equationsüConversions between grams and moles

MOLE RATIO

§Mole ratio: a conversion factor that converts moles of one compound in a balanced chemical equation into moles of another compound

§Ex: __ H2 + ___ O2 à ___ H2O§2 mol H2: 1 mol O2

2 mol H2 : 2 mol H2O 1 mol O2: 2 mol H2 etc…

2 1 2

STOICHIOMETRY STEPS

① Write a balanced chemical equation.② Identify known & unknown.③ Line up conversion factors.

§ - Mole ratio: mole « moles§ - Molar mass: moles « grams§ - Molarity: moles « liters solution§ - Molar volume: moles « liters gas

④ Double check your answer. Molar Volume

1 mole of gas = 22.4 L at STP- STP = Standard Temperature &

Pressure- 0°C and 1 atm

Stoichiometry Map

When in doubt, convert to moles!

SAMPLE PROBLEM (MOLE TO MOLE)

How many moles of KClO3 must decompose in order to produce 9 moles of oxygen gas?

___ KClO3 à ___ KCl + ___O2

§Given: 9 mol O2§Unknown: ? mol KClO3

9 mol O2 2 mol KClO3

3 mol O2

2 2 3

= 6 mol KClO3

YOU TRY!

§Mg reacts with HCl according to the following equation:Mg + HCl à MgCl2 + H2

If 2 moles of HCl react with Mg, how many moles of H2 will be produced?§1 mol H2

§Two atoms of sulfur react with three molecules of oxygen to form two molecules of sulfur trioxide. How many moles of sulfur react to produce 6 moles of SO3?§2 S + 3 O2 à 2 SO3§6 mol S

SAMPLE PROBLEM (MOLE TO MASS)

In photosynthesis, plants use energy from the sun to produce glucose, C6H12O6, and oxygen from the reaction of carbon dioxide and water. What mass, in grams of glucose (C6H12O6) is produced when 3.00 mol of H2O react with CO2?

____ CO2 + ____ H2O à ____ C6H12O6 + ____ O2

= 90.1 g C6H12O6

6 6 1 6

3.00 mol H2O 1 mol C6H12O6 180.18 g C6H12O6

6 mol H2O 1 mol C6H12O6

YOU TRY!

§ When sodium azide is activated in an car airbag, nitrogen gas and sodium are produced according to the following equation:

NaN3 à Na + N2If 0.500 mol of NaN3 react, what mass in grams of nitrogen would result?§ Answer: 21.0 g Na

§ When magnesium burns in air, it combines with oxygen to form magnesium oxide according to the following equation:

Mg + O2 à MgOWhat is the mass in grams of MgO produced from 2.00 moles of magnesium?§ 80.6 g MgO

Review

____ Li + ____ Br2 à ____ LiBr§How many moles of Li are reacted when 4 moles of LiBr are

formed in the reaction?§2 Li + Br2 à 2 LiBr§4 mol Li

§How many grams of Br2 are formed from the same reaction?§320 g Br2

SAMPLE PROBLEM (MASS TO MASS)

Tin(II) fluoride, SnF2, is used in some toothpastes. It is made by the reaction of tin with hydrogen fluoride according to the following equation:

Sn + 2 HF à SnF2 + H2How many grams of SnF2 are produced from the reaction of 30.00 g of HF with Sn?

§= 123.6 g SnF2

30.00 g HF 1 mol HF 1 mol SnF2 156.7 g SnF2

19.01 g HF 2 mol HF 1 mol SnF2

YOU TRY!

Laughing gas is sometimes used as an anesthetic in dentistry. It is produced in the following reaction:

NH4NO3 à N2O + 2 H2O§ How many grams of NH4NO3 are required to produce 33.0

g of N2O?§ 60.0 g NH4NO3

§ How many grams of water are produced in this reaction?§ 27.0 g H2O