CHAPTER 3CHAPTER 3

Stoichiometry Calculations Stoichiometry Calculations With Chemical Formulas With Chemical Formulas

&Equations&EquationsThe Real Deal

Chemical EquationsChemical Equations

Stoichiometry – literal meaning Stoichiometry – literal meaning “measurement of elements”“measurement of elements”

Chemical reactions are expressed Chemical reactions are expressed equationsequations

“ “+” means reacts with+” means reacts with means producesmeans produces

Numbers in front of elements & Numbers in front of elements & compounds are called coefficients compounds are called coefficients (1s are not written) (1s are not written)

NN22 + 2O + 2O22 2NO 2NO22

one None N22 reacts with 2O reacts with 2O22s to make 2NOs to make 2NO22ss

Chemical EquationsChemical Equations

Balancing EquationsBalancing Equations

NN22 + 2O + 2O22 2NO 2NO22

Multiply coefficients and subscripts to Multiply coefficients and subscripts to get the number of atoms for each get the number of atoms for each elementelement

The number on the left side of the The number on the left side of the arrow must equal the number on the arrow must equal the number on the rightright

Chemical EquationsChemical Equations

LEFTLEFTN: 1 times 2 for 2 nitrogensN: 1 times 2 for 2 nitrogens

O: 2 times 2 for 4 oxygensO: 2 times 2 for 4 oxygens RightRight

N: 2 times 1 for 2 nitrogensN: 2 times 1 for 2 nitrogens

O: 2 times 2 for 4 oxygensO: 2 times 2 for 4 oxygens

Chemical EquationsChemical Equations11NN22 + 2O + 2O22 2N 2N11OO22

Iron III Oxide: FeIron III Oxide: Fe22OO33

□□Fe + Fe + □□OO22 □□FeFe22OO33

2 Irons are needed on the right…but more 2 Irons are needed on the right…but more importantly so are 3 Oxygens and they only importantly so are 3 Oxygens and they only come 2 in a package so 3O2 give 6 oxygenscome 2 in a package so 3O2 give 6 oxygens

□□Fe + 3OFe + 3O22 2Fe2Fe22OO33

Now we have 6 Os on both sides, so we balance Now we have 6 Os on both sides, so we balance the Fe. There are 2 x 2 =4 on the right so…the Fe. There are 2 x 2 =4 on the right so…

4Fe + 3O4Fe + 3O22 2Fe2Fe22OO33

Chemical EquationsChemical Equations

Adding states to reactants & Adding states to reactants & productsproducts

(s) for solid(s) for solid

(l) for liquid(l) for liquid

(g) for gas(g) for gas

(aq) for things dissolved in water (aq) for things dissolved in water

Chemical EquationsChemical Equations

Combustion Reactions – Elements or Combustion Reactions – Elements or compounds reacting with oxygencompounds reacting with oxygen

Rapid & make a flame (not always visible)Rapid & make a flame (not always visible)

CC66HH1414 + O + O22 CO CO22+H+H22O O Look @ single Os first!!! 14Hs=7 water, can’t have Look @ single Os first!!! 14Hs=7 water, can’t have

odd Os, they come in two packs – so double it to odd Os, they come in two packs – so double it to 14 & 2x the octane14 & 2x the octane

2C2C66HH1414 + O + O22 12 CO12 CO22+14H+14H22O O

24+14= 38 O or 19 O24+14= 38 O or 19 O22

2C2C66HH1414 + 19O + 19O22 12 CO12 CO22+14H+14H22OO

Chemical EquationsChemical Equations

Formula weights are the sum of the Formula weights are the sum of the atomic weights of ALL the elements in atomic weights of ALL the elements in a formulaa formula

IF the molecule is not ionic or IF the molecule is not ionic or dissolves in water the molecular dissolves in water the molecular weight is the formula weightweight is the formula weight

Who cares what the book says, in Who cares what the book says, in here we will always call it molecular here we will always call it molecular weight!!weight!!

Formula WeightsFormula Weights

Pb(CrOPb(CrO44))

Formula WeightsFormula Weights