Chemical ReactionsChemical Reactions

Writing Formulas: Review

carbon tetrafluoride CF4

Na3PO4sodium phosphate

Cu2SO4cuprous sulfateAnalysis If “Yes”

The compound is covalent: the

prefixes give the subscripts.

* Are there prefixes present

The compound is ionic:

subscripts must be

determined by balancing charges

prefixes covalent prefixes indicate subscripts

metal ionic balance charges 3 Na1+ needed for 1 PO43-

metal present ionic balance charges 2 Cu1+ needed for 1 SO42-

Al2S3aluminum sulfidemetal present ionic balance charges 2 Al3+ needed for 3 S2-

N2O5dinitrogen pentoxideprefixes covalent prefixes indicate subscripts

NH4NO3ammonium nitratepolyatomic ion present ionic balance charges

1 NH41+ needed for 1 NO3

1-

PbO2plumbic oxidemetal present ionic balance charges 1 Pb4+ needed for 2 O2-

Fe2(CO3)3 ferric carbonatemetal present ionic balance charges 2 Fe3+ needed for 3 CO3

2-

Indicators of a Chemical Change

Precipitate

Color Change

Gas Given off

Temperature Change

Light Produced

• In a chemical reaction, In a chemical reaction, reactantsreactants are chemically are chemically combinedcombined

or broken down to make (produce) or broken down to make (produce) productsproducts..• arrow always points toward arrow always points toward productsproducts!!

CHCH4(g)4(g) + 2O + 2O2(g)2(g) CO CO2(g)2(g) + 2H + 2H22OO(l)(l)

reactantreactantss

productproductss

Reactants vs. Products

(s)(s) solidsolid

(l)(l) liquidliquid

(g)(g) gasgas

(aq)(aq) aqueous (dissolved in aqueous (dissolved in water)water)

yielyieldsds

- a whole number that is placed before a - a whole number that is placed before a symbol of an element or formula of a symbol of an element or formula of a compound in order to balance a chemical compound in order to balance a chemical equation. A coefficient multiplies the entire equation. A coefficient multiplies the entire formula by that whole number.formula by that whole number.

Example - Example - 22 Al + Al + 66 HCl HCl 22 AlClAlCl33 + + 33 H H22

2 Al 2 Al 2Al2Al 6H 6H 6H 6H 6Cl 6Cl 6Cl 6Cl

CoefficientCoefficient

Diatomic ElementsDiatomic Elements

- there are seven elements that exist as - there are seven elements that exist as diatomic molecules in which two atoms of diatomic molecules in which two atoms of the same element bond together.the same element bond together.

Br I N Cl H O F Br I N Cl H O F Whenever these elements appear as free Whenever these elements appear as free

elements (by themselves) in a chemical elements (by themselves) in a chemical equation, they MUST have a subscript "2" equation, they MUST have a subscript "2" written beside them.written beside them.

Example 1 - 2 HExample 1 - 2 H22 + O + O22 2H2H22OO Example 2 - 2 Na + ClExample 2 - 2 Na + Cl22 2NaCl 2NaCl Example 3 - 3 HExample 3 - 3 H22 + N + N22 2NH 2NH33

Writing Chemical Writing Chemical EquationsEquations

Sometimes chemical equations are written Sometimes chemical equations are written using the names of the free elements and using the names of the free elements and compounds. But, usually chemical equations compounds. But, usually chemical equations are written with symbols for free elements are written with symbols for free elements and formulas for compounds instead of and formulas for compounds instead of names.names.

Examples:Examples: magnesium + hydrochloric acid magnesium + hydrochloric acid magnesium magnesium

chloride + hydrogenchloride + hydrogen Mg + 2 HCl Mg + 2 HCl MgCl MgCl22 + H + H22

sodium + water sodium + water sodium hydroxide + hydrogen sodium hydroxide + hydrogen 2Na+ 2H2Na+ 2H22O O 2 NaOH + H 2 NaOH + H22

• There are five different types of reactions…There are five different types of reactions…

• 1. SYNTHESIS or COMBINATION…1. SYNTHESIS or COMBINATION… - two or more reactants combine to produce - two or more reactants combine to produce oneone product.product.• Ex…Ex…

MgMg (s) (s) + O + O2 (g)2 (g) MgO MgO (s)(s)

CaOCaO (s) (s) + CO + CO2 (g)2 (g) CaCO CaCO33 (s)(s)

KNOKNO2 (s)2 (s) + O + O2 (g)2 (g) KNO KNO33 (s)(s)

22 22 2:1 2:1 221:1 1:1 112:1 2:1 22

22 22

Types of Reactions

• 2. DECOMPOSITION…2. DECOMPOSITION… - opposite of - opposite of synthesissynthesis - A single compound (- A single compound (oneone)) reactant breaks reactant breaks down down (decomposes) into two or more (decomposes) into two or more elements or new elements or new compounds (products).compounds (products).• Ex…Ex…

HgO Hg + OHgO Hg + O22 22 22 2 2 2:12:1

HNOHNO33 N N22OO5 5 ++ HH22OO 22 2 2 1:11:1

Types of Reactions

• 3. SINGLE DISPLACEMENT…3. SINGLE DISPLACEMENT… - one element in a compound is displaced - one element in a compound is displaced (kicked out) by another(kicked out) by another(more reactive) element.(more reactive) element.

• Ex…Ex…

Mg + Zn(NOMg + Zn(NO33))22 Mg(NOMg(NO33))22 + Zn + Zn 1:1 1:1 1:11:1

ClCl22 + KI + KI KCl + IKCl + I22 22 22 1:2 2:11:2 2:1

** metals can only replace metals and vice versa for ** metals can only replace metals and vice versa for non-metals!non-metals!

- reactants =1element &1compound …products - reactants =1element &1compound …products = 1element &= 1element &1compound.1compound.

-- By definition, all single replacement reactions By definition, all single replacement reactions are redox reactionsare redox reactions

Types of Reactions

• 4. DOUBLE DISPLACEMENT…4. DOUBLE DISPLACEMENT… - cations of two different compounds trade places.- cations of two different compounds trade places. - reactants = 2 compounds …products = 2 different - reactants = 2 compounds …products = 2 different compounds compounds• Ex…Ex…

NaCl + AgNONaCl + AgNO33 AgCl + NaNOAgCl + NaNO33 1:1 1:1 1:11:1

Ca(OH)Ca(OH)22 + H + H33POPO44 H(OH) + CaH(OH) + Ca33(PO(PO44))22(H(H22O)O)

33 66 22

3:2 6:13:2 6:1

Types of Reactions

• 5. COMBUSTION…5. COMBUSTION…

- generally involves the burning of a hydrocarbon.- generally involves the burning of a hydrocarbon. - fires generally need oxygen to burn (reactant).- fires generally need oxygen to burn (reactant). - fires generally release water and carbon dioxide - fires generally release water and carbon dioxide (prod).(prod). - reactants = hydrocarbon and O- reactants = hydrocarbon and O22 …products = H …products = H22O O and COand CO22

CC33HH88 + O + O22 CO CO22 + H + H22OO 33 44 55 1:5 1:5 3:43:4

• Ex…Ex…

CC66HH1212OO66 + O + O22 CO CO22 + H + H22OO 66 66 66

1:6 1:6 6:66:6

- oxygen combines with a substance and releases - oxygen combines with a substance and releases energy in the form of heat and light.energy in the form of heat and light.

Types of Reactions

• identify the following types of identify the following types of rxns…rxns… Pb(NOPb(NO33))22 + K + K22CrOCrO44 PbCrOPbCrO44 + 2KNO + 2KNO33

double displacementdouble displacement

2Al(OH)2Al(OH)33 AlAl22OO33 + 3H + 3H22OO decompositiondecomposition

CHCH44 + 2O + 2O22 COCO22 + 2H + 2H22OO combustioncombustion

4Li + O4Li + O22 2Li2Li22OO synthesissynthesis

2Al + 3CuSO2Al + 3CuSO44 AlAl22(SO(SO44))33 + 3Cu + 3Cu single displacementsingle displacement

Types of Reactions

Balancing Chemical Equations

Balancing Equations

• chemical equations need to be balanced to chemical equations need to be balanced to comply w/ thecomply w/ theLaw of Conservation of Mass.Law of Conservation of Mass.(matter cannot be (matter cannot be

created orcreated ordestroyed)destroyed)

• # of atoms for each element must = each other # of atoms for each element must = each other on both sides of rxn.on both sides of rxn.

** use coefficients to balance.** use coefficients to balance.

- must be whole #s- must be whole #s

- large # in front of - large # in front of compoundcompound

- indicate the mole ratio each time you - indicate the mole ratio each time you balance!balance!• start from far left and work your way to the right!start from far left and work your way to the right!

OO2 (g)2 (g) + H + H2 (g)2 (g) H H22O O (l)(l)

• Practice…Practice…

22222 O 2 O atomsatoms

1 O atom1 O atom4 H 4 H atomsatoms

Mole Ratio = 1:2 2Mole Ratio = 1:2 2

FeFe (s) (s) + O + O2 (g)2 (g) Fe Fe22OO33 (s)(s)22 223344

Mole Ratio = 4:3 2Mole Ratio = 4:3 2

Balancing Equations

• Practice…Practice…

HH22OO2 (aq)2 (aq) O O2 (g)2 (g) + H + H22O O (l)(l)2222Mole Ratio = 2 1:2Mole Ratio = 2 1:2

AgNOAgNO3 3 + H+ H22S AgS Ag22SS + HNO + HNO3322 22

Mole Ratio = 2:1 1:2Mole Ratio = 2:1 1:2** balance polyatomics ** balance polyatomics together!together!

MnOMnO2 2 + HCl MnCl+ HCl MnCl2 2 + H + H22O + ClO + Cl222244

Mole Ratio = 1:4 Mole Ratio = 1:4 1:2:11:2:1

Balancing Equations