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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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slide1

Chemistry

Unit 7:

Chemical Equations

slide2

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

slide3

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.

slide4

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

slide5

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

slide6

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

slide7

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)

slide9

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

=

slide10

+

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…

+

slide11

+

___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.

slide12

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)

slide13

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

slide14

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

slide15

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

slide16

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

slide17

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

slide18

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

+

+

slide19

_ 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

slide20

_ 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)

slide21

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

slide22

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…

slide23

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)

slide24

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)

slide25

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.

slide26

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

slide27

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.

**

slide28

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)

slide29

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

slide30

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