Chemical Equations

Chemistry

Evidence of a chemical reaction:

A reaction has occurred if the chemical and physical

properties of the reactants and products differ.

heatlight

soundgas emittedcolor change

odor

For a reaction to occur,particles of reactantsmust collide, and withsufficient energy

collision theory

activation energy:

Chemical reactions release or absorb energy.

energy needed to start a reaction

exothermicreactions

endothermicreactions

The reaction in an oxy-acetylene torch is exothermic.

Photosynthesis is anendothermic reaction.

catalyst: speeds up reaction wo/being consumed

… it lowers the activation energy (AE)

AEAE

time time

without catalyst with catalyst

Examples: enzymes catalyze biochemical reactions

catalytic converters convert CO into CO2

En

erg

y

Reaction Conditions and Terminology

Certain symbols give more info about a reaction.

(s) = solid

(l) = liquid

(g) = gas

(aq) = aqueous(dissolved in H2O) NaCl(s) NaCl(aq)

More on aqueous…

-- “soluble” or “in solution” also indicate that a substance is dissolved in water (usually)

-- acids are aqueous solutions

Other symbols…

means...

Temp. at which we perform rxn. might be given.

The catalyst used might be given.

means ______ is added to the reaction

MgCO3(s) MgO(s) + CO2(g)

C2H4(g) + H2(g) C2H6(g) Pt

C6H5Cl + NaOH C6H5OH + NaCl 400oC

“yields” or “produces”

heat

(i.e., clues about the reaction)

precipitate: a solid product that forms in an aqueous solution reaction

Na2CO3 + Ca(NO3)2 CaCO3 +(aq) (aq)

Na1+Ca2+CO3

2–

NO31–

2 (aq)(s)

Na1+

NaNO3

NO31–

ppt

clearNa2CO3

solution

clearCa(NO3)2

solution

cloudy solutioncontaining CaCO3(s)

and NaNO3(aq)

“chunks”“sinkies”“floaties”

Factors that influencethe rate of a reaction

To make reactionrate increase…

concentration of reactants

particle size

temperature

mechanical mixing

pressure

catalyst use onenature of reactants N/A

In a reaction:

atoms are rearranged

AND mass

energy

charge

are conserved

Balancing Chemical Equations

=law of

conservationof mass

same # of atomsof each type on each

side of equation

EX. solid iron reacts with oxygen gas to yieldsolid iron (III) oxide

If all coefficients are 1…

If we change subscripts…

Fe3+ O2–

___Fe(s) + ___O2(g) ___Fe2O3(s)

+

___Fe(s) + ___O2(g) ___Fe2O3(s) 11 1

___Fe2(s) + ___O3(g) ___Fe2O3(s) 11 1

+

Changing a ___________ changes the substance.

To balance, modify only _____________.

Right now, _______________ don’t enter intoour “balancing” picture.

subscript

coefficients

superscripts

___Fe(s) + ___O2(g) ___Fe2O3(s)

+

23

Hint: Start with most complicated substances firstand leave simplest substances for last.

4

2

solid sodium reacts w/oxygento form solid sodium oxide

___O2(g)___Na(s) ___Na2O(s)+

Na1+ O2–

+

14

Aqueous aluminum sulfate reacts w/aqueous calciumchloride to form a white precipitate of calcium sulfate.The other compound remains in solution.

Al3+ SO42– Ca2+ Cl1–

_ Al2(SO4)3(s)+ _ CaCl2 _ CaSO4 _ AlCl3(aq) (aq) (aq)+1 33 2

1

1

Methane gas (CH4) reacts withoxygen to form carbon dioxidegas and water vapor.

_ CH4(g) + _ O2(g) _ CO2(g) _ H2O(g)+2 1 2

_ CaC2(s) + _ H2O(l) _ C2H2(g) + _ CaO(s)

_ CaSi2 + _ SbI3 _ Si + _ Sb + _ CaI2

_ Al + _ CH3OH _ Al(CH3O)3 + _ H2

1 1 1

3 2 26 3

3262 13

Furnaces burnprimarily methane.

2_ C2H2(g) + _ O2(g) _ CO2(g) + _ H2O(l) ** 5 4 21 2 1

1_ C3H8 + _ O2 _ CO2 + _ H2O ** 5 3 4

1_ C5H12 + _ O2 _ CO2 + _ H2O ** 8 5 6

** = complete combustion of a hydrocarbonyields CO2 and H2O

Write equations for the combustionof C7H16 and C8H18.

1_ C7H16 + _ O2 _ CO2 + _ H2O 11 7 8

1_ C8H18 + _ O2 _ CO2 + _ H2O 25 8 92 16 18

Classifying Reactions

four types

synthesis: simpler substances combine to form more complex substances

oxygen + rhombic sulfur sulfur dioxide

sodium + chlorine gas sodium chloride

A + B AB AB + C ABC A + B + C ABC

__ O2 __ S8+ __ SO2

__ Na __ Cl2+ __ NaCl

8 1 8

2 1 2

decomposition: complex substances are broken down into simpler ones

lithium chlorate lithium chloride + oxygen

water hydrogen gas + oxygen gas

Li1+ ClO31– Li1+ Cl1–

_ LiClO31 _ LiCl + _ O2

12 2 3

_ H2O2 _ H2 + _ O22 1

AB A + B ABC AB + C ABC A + B + C

single-replacement: one elementreplaces another

AB + C A + CB AB + C B + AC

chlorine sodium

bromide sodium

chloride bromine + +

? aluminum copper (II)

sulfate +

_ Cl2 Na1+ Br1–

_ NaBr1 _ Br2 +

Na1+ Cl1–

_ NaCl +2 2 1

Cu2+ SO42–

_ CuSO4_ Al +

Al3+ SO42–

_ Al2(SO4)31 _ Cu+32 3

copper aluminumsulfate +

double-replacement:

AD + CBAB + CD

iron (III)chloride

+potassiumhydroxide

?

Fe3+ Cl1–

_ FeCl3 +1

K1+ OH1–

_ KOH

Fe3+ OH1– K1+ Cl1–

_ KCl_ Fe(OH)3 +3 1 3

iron (III)hydroxide

+potassiumchloride

lead (IV)nitrate

+calciumoxide

?

Pb4+ O2–

_ Pb(NO3)4 +1

Ca2+ NO31–

_ CaO _ Ca(NO3)2_ PbO2 +2 1 2

Pb4+ O2– Ca2+ NO31–

lead (IV)oxide

+calciumnitrate

1

How do we know if a reaction will occur?

For single-replacement reactions, use Activity Series.In general, elements above replace elements below.

_ Ba + _ FeSO4

_ Mg + _ Cr(ClO3)3

_ Pb + _ Al2O3

_ NaBr + _ Cl2

_ FeCl3 + _ I2

_ CoBr2 + _ F2

_ Fe + _ BaSO4

_ Cr + _ Mg(ClO3)2

NR

_ NaCl + _ Br2

NR

_ CoF2 + _ Br2

1 1 1

3 2 2 3

2 1

1 1

2 1

1 1

(?)

For double-replacement reactions,reaction will occurif any product is: water a gas a precipitate

driving forces

_ Pb(NO3)2(aq) + _ KI(aq)

_ KOH(aq) + _ H2SO4(aq)

_ FeCl3(aq) + _ Cu(NO3)2(aq)

H1+ OH1–

Fe3+ Cl1– NO31–

Pb2+ NO31– K1+ I1– Pb2+ NO3

1– K1+ I1–

Check new combinations to decide.

(?)

K1+ SO42–

Cu2+

H1+ OH1– K1+ SO42– (?) (?)

Cl1–

Cu2+ (?)

Fe3+ NO31– (?)

(ppt) (aq)

(aq) (water)

(aq) (aq)

NR

_ K2SO4(aq) + _ H2O(l)

_ PbI2(s) + _ KNO3(aq) 1 2 1 2

2 1 1 2

Ions in Aqueous Solution

Pb(NO3)2(s) Pb(NO3)2(aq)

Pb2+(aq) + 2 NO31–(aq)

addwater

dissociation:

Pb2+NO3

1–

NO31–

Pb2+

NO31–

NO31–

“splitting into ions”

NaI(s) NaI(aq)

Na1+(aq) + I1–(aq)

Na1+ I1– Na1+ I1–add

water

Mix them and get the overall ionic equation…

__Pb2+(aq) + __NO31–(aq) + __Na1+(aq) + __I1–(aq)

__PbI2(s) + __NO31–(aq) + __Na1+(aq) yields

reactants

products

Cancel spectator ions to get net ionic equation…

__PbI2(s)1

1 2 2 2

221

Pb2+

NO31–

NO31– Na1+ I1–

NO31–

NO31–

Na1+ I1–

Na1+

Na1+

__Pb2+(aq) + __I1–(aq) 1 2

Pb2+I1–

I1–

Pb2+I1–

I1–

Pb2+

I1–

I1–

Mix together Zn(NO3)2(aq) and Ba(OH)2(aq):

Zn(NO3)2(aq) Ba(OH)2(aq)

Zn2+(aq) + 2 NO31–(aq) Ba2+(aq) + 2 OH1–(aq)

Ba2+

OH1–

OH1–

Zn2+

NO31–

NO31–

clear Zn(NO3)2 solution clear Ba(OH)2 solution

Mix them and get the overall ionic equation…

__Zn2+(aq) + __NO31–(aq) + __Ba2+(aq) + __OH1–(aq)

__Zn(OH)2(s) + __NO31–(aq) + __Ba2+(aq) yields

reactants

products

Cancel spectator ions to get net ionic equation…

__Zn(OH)2(s)1

1 2 1 2

121

Zn2+

NO31–

NO31– OH1–

NO31–

NO31–

__Zn2+(aq) + __OH1–(aq) 1 2

Zn2+

OH1–

Ba2+

Ba2+Zn2+

OH1–

OH1–

OH1–

OH1–

Zn2+OH1–

OH1–

Polymers and Monomers

polymer: a large molecule (often a chain) made of many smaller molecules called monomers

Polymers can be made more rigid if the chains arelinked together by way of a cross-linking agent.

Monomer Polymer

amino acids…………

nucleotides (w/N-bases A,G,C,T/U)…..

styrene………………

PVA………………….

proteins

nucleic acids

polystyrene

“slime”

polyvinylalcohol

H–N–C–C–O–H

H H O

R

Quantitative Relationships in Chemical Equations

4 Na(s) + O2(g) 2 Na2O(s)

Particles 4 atoms 1 m’cule 2 m’cules

Moles 4 mol 1 mol 2 mol

Grams 4 g 1 g 2 g

** Coefficients of a balanced equation represent# of particles OR # of moles,but NOT # of grams.

When going from moles of one substance to molesof another, use coefficients from balanced equation.

part.

vol.

mass

MOL

mass

vol.

part.

MOL

SUBSTANCE “A” SUBSTANCE “B”

(known) (unknown)

Use coeff. from balancedequation in crossing this bridge

4 Na(s) + 1 O2(g) 2 Na2O(s)

4 Na(s) + O2(g) 2 Na2O(s)

How many moles oxygen will react with 16.8 moles sodium?

How many moles sodium oxide are produced from87.2 moles sodium?

How many moles sodium are requiredto produce 0.736 moles sodium oxide?

( )4 mol Na

1 mol O216.8 mol Na = 4.2 mol O2

87.2 mol Na = 43.6 mol Na2O

( )2 mol Na2O

4 mol Na0.736 mol Na2O = 1.472 mol Na

( )2 mol Na2O

4 mol Na

O2Na Na2ONa2O Na

0 0