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Chemistry. Unit 7: Chemical Equations. For a reaction to occur, particles of reactants must collide, and with sufficient energy. Evidence of a chemical reaction:. odor. light. heat. gas emitted. sound. color change. A reaction has occurred if the chemical and physical

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Chemistry

Unit 7:

Chemical Equations


For a reaction to occur,

particles of reactants

must collide, and with

sufficient energy

Evidence of a chemical reaction:

odor

light

heat

gas emitted

sound

color change

A reaction has occurred if the chemical and physical

properties of the reactants and products differ.

collision theory


exothermic

reactions

endothermic

reactions

The reaction in an oxy-

acetylene torch is exothermic.

Photosynthesis is an

endothermic reaction.

energy needed to start a reaction

activation energy:

Chemical reactions release or absorb energy.


AE

AE

catalyst: speeds up reaction wo/being consumed

it lowers the activation energy (AE)

without catalyst

with catalyst

Energy

time

time

Examples:

enzymes catalyze biochemical reactions

catalytic converters convert CO into CO2


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


means...

means ______ is added to the reaction

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

C6H5Cl + NaOH C6H5OH + NaCl

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

Other symbols…

(i.e., clues about the reaction)

“yields” or “produces”

heat

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

400oC

The catalyst used might be given.

Pt


clear

Na2CO3

solution

clear

Ca(NO3)2

solution

precipitate: a solid product that forms in an

aqueous solution reaction

(aq)

(aq)

Na2CO3 + Ca(NO3)2

(aq)

(s)

2

NaNO3

CaCO3 +

“chunks”

NO31–

Na1+

“sinkies”

Ca2+

CO32–

NO31–

Na1+

“floaties”

ppt

cloudy solution

containing CaCO3(s)

and NaNO3(aq)


In a reaction:

atoms are rearranged

mass

AND

are conserved

energy

charge

Balancing Chemical Equations

law of

conservation

of mass

same # of atoms

of each type on each

side of equation

=


+

1

1

1

___Fe2(s)

___O3(g)

___Fe2O3(s)

EX. solid iron reacts with oxygen gas to yield

solid iron (III) oxide

Fe3+

O2–

+

___Fe(s)

___O2(g)

___Fe2O3(s)

If all coefficients are 1…

+

1

1

1

___Fe(s)

___O2(g)

___Fe2O3(s)

+

If we change subscripts…

+


+

___Fe(s)

___O2(g)

___Fe2O3(s)

subscript

Changing a ___________ changes the substance.

coefficients

To balance, modify only _____________.

superscripts

Right now, _______________ don’t enter into

our “balancing” picture.

4

3

2

+

Hint: Start with most complicated substances first

and leave simplest substances for last.


solid sodium reacts w/oxygen

to form solid sodium oxide

Na1+

O2–

4

1

2

___Na(s)

+

___O2(g)

___Na2O(s)

+

Aqueous aluminum sulfate reacts w/aqueous calcium

chloride to form a white precipitate of calcium sulfate.

The other compound remains in solution.

Ca2+

Al3+

SO42–

Cl1–

1

3

3

2

+

+

_ AlCl3

_ CaSO4

_ Al2(SO4)3

_ CaCl2

(aq)

(s)

(aq)

(aq)


Furnaces burn

primarily methane.

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

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

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

Methane gas (CH4) reacts with

oxygen to form carbon dioxide

gas and water vapor.

1

2

1

2

_ CH4(g)

_ O2(g)

_ H2O(g)

_ CO2(g)

+

+

1

1

1

1

3

2

6

2

3

3

1

2

6

2

3


1

2

1

2

5

4

2

_ C2H2(g) + _ O2(g) _ CO2(g) + _ H2O(l)

**

1

5

3

4

_ C3H8 + _ O2 _ CO2 + _ H2O

**

1

8

5

6

_ C5H12 + _ O2 _ CO2 + _ H2O

**

complete combustion of a hydrocarbon

yields CO2 and H2O

** =

Write equations for the combustion

of C7H16 and C8H18.

1

11

7

8

_ C7H16 + _ O2 _ CO2 + _ H2O

1

25

8

9

2

16

18

_ C8H18 + _ O2 _ CO2 + _ H2O


four types

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

Classifying Reactions

synthesis: simpler substances combine to form

more complex substances

oxygen + rhombic sulfur sulfur dioxide

8

1

8

+

__ O2

__ SO2

__ S8

sodium + chlorine gas sodium chloride

+

__ Na

2

1

__ NaCl

2

__ Cl2


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

lithium chlorate lithium chloride + oxygen

water hydrogen gas + oxygen gas

decomposition: complex substances are broken

down into simpler ones

Li1+

Li1+

ClO31–

Cl1–

2

2

1

1

3

+ _ O2

_ LiClO3

_ LiCl

2

2

1

+ _ O2

_ H2O

_ H2


AB + C A + CB

AB + C B + AC

sodium

bromide

sodium

chloride

chlorine

bromine

+

+

copper (II)

sulfate

aluminum

sulfate

aluminum

copper

+

+

single-replacement:

one element

replaces another

Na1+

Na1+

Br1–

Cl1–

1

2

2

1

_ Cl2

_ Br2

_ NaBr

_ NaCl

+

+

?

Cu2+

SO42–

Al3+

SO42–

+

+

2

3

1

3

_ Al

_ CuSO4

_ Cu

_ Al2(SO4)3


iron (III)

chloride

iron (III)

hydroxide

potassium

hydroxide

potassium

chloride

+

+

AB + CD

lead (IV)

nitrate

lead (IV)

oxide

calcium

oxide

calcium

nitrate

+

+

double-replacement:

AD +

CB

?

Fe3+

Fe3+

Cl1–

Cl1–

K1+

OH1–

OH1–

K1+

1

3

1

3

_ FeCl3

_ KOH

_ Fe(OH)3

_ KCl

+

+

?

Pb4+

Pb4+

O2–

O2–

NO31–

Ca2+

Ca2+

NO31–

1

2

1

2

_ Pb(NO3)4

_ CaO

_ PbO2

_ Ca(NO3)2

+

+


_ Ba + _ FeSO4

_ Mg + _ Cr(ClO3)3

_ Pb + _ Al2O3

_ NaBr + _ Cl2

_ FeCl3 + _ I2

_ CoBr2 + _ F2

How do we know if a reaction will occur?

For single-replacement reactions, use Activity Series.

In general, elements above replace elements below.

1

1

1

1

_ Fe + _ BaSO4

3

2

2

3

_ Cr + _ Mg(ClO3)2

NR

_ NaCl + _ Br2

2

1

2

1

NR

1

1

1

1

_ CoF2 + _ Br2


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

_ KOH(aq) + _ H2SO4(aq)

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

(?)

(?)

Fe3+

Cu2+

Cl1–

NO31–

For double-replacement reactions,

reaction will occur

if any product is:

water a gas a precipitate

driving forces

Check new combinations to decide.

1

2

1

2

_ PbI2(s) + _ KNO3(aq)

(?)

(?)

Pb2+

Pb2+

I1–

I1–

NO31–

K1+

K1+

NO31–

(ppt)

(aq)

_ K2SO4(aq) + _ H2O(l)

2

1

1

2

(?)

(?)

K1+

OH1–

H1+

SO42–

K1+

SO42–

H1+

OH1–

(aq)

(water)

NR

Fe3+

Cu2+

Cl1–

NO31–

(aq)

(aq)


NO31–

NO31–

Pb2+

Pb2+

NO31–

NO31–

I1–

Na1+

Na1+

I1–

Ions in Aqueous Solution

Pb(NO3)2(aq)

Pb(NO3)2(s)

Pb2+(aq) + 2 NO31–(aq)

add

water

dissociation:

“splitting into ions”

NaI(aq)

NaI(s)

Na1+(aq) + I1–(aq)

add

water


yields

1

2

1

__Pb2+(aq) + __I1–(aq)

__PbI2(s)

I1–

I1–

I1–

I1–

I1–

I1–

I1–

I1–

NO31–

NO31–

Na1+

Na1+

Na1+

Na1+

Pb2+

Pb2+

Pb2+

Pb2+

NO31–

NO31–

Mix them and get the overall ionic equation…

reactants

1

2

2

2

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

1

2

2

+ __NO31–(aq) + __Na1+(aq)

__PbI2(s)

products

Cancel spectator ions to get net ionic equation…


OH1–

NO31–

clear Zn(NO3)2 solution

clear Ba(OH)2 solution

Ba2+

Zn2+

OH1–

NO31–

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)


OH1–

OH1–

OH1–

OH1–

NO31–

yields

OH1–

OH1–

OH1–

OH1–

NO31–

Zn2+

Zn2+

Ba2+

Ba2+

Zn2+

Zn2+

NO31–

NO31–

Mix them and get the overall ionic equation…

reactants

1

2

1

2

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

1

2

1

+ __NO31–(aq) + __Ba2+(aq)

__Zn(OH)2(s)

products

Cancel spectator ions to get net ionic equation…

1

2

1

__Zn2+(aq) + __OH1–(aq)

__Zn(OH)2(s)


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 are

linked together by way of a cross-linking agent.


H H O

H–N–C–C–O–H

R

Monomer

Polymer

aminoacids…………

proteins

nucleotides (w/N-

bases A,G,C,T/U)…..

nucleic acids

styrene………………

polystyrene

PVA………………….

“slime”

polyvinyl

alcohol


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

Quantitative Relationships in Chemical Equations

Coefficients of a balanced equation represent

# of particles OR # of moles,

but NOT # of grams.

**


mass

mass

vol.

vol.

MOL

MOL

part.

part.

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

When going from moles of one substance to moles

of another, use coefficients from balanced equation.

Use coeff. from balanced

equation in crossing this bridge

SUBSTANCE “B”

SUBSTANCE “A”

(unknown)

(known)


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

(

)

(

(

)

)

Na2O

Na

Na2O

Na

O2

How many moles oxygen will react with 16.8 moles sodium?

1 mol O2

16.8 mol Na

= 4.2 mol O2

4 mol Na

How many moles sodium oxide are produced from

87.2 moles sodium?

2 mol Na2O

87.2 mol Na

= 43.6 mol Na2O

4 mol Na

How many moles sodium are required

to produce 0.736 moles sodium oxide?

4 mol Na

0.736 mol Na2O

= 1.472 mol Na

2 mol Na2O


0

0


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