Chemical Equations & Reactions - PowerPoint Presentation

Slide1

Chemical Equations & ReactionsSlide2

Chemical Equations

This equation means:

4 Al(

s

) + 3 O

2(g) 2 Al2O3(s)

4 Al atoms + 3 O

2 molecules yield 2 molecules of Al2O3

4 Al moles + 3 O2 moles yield 2 moles of Al2O3

or

4 g Al + 3 g O2 yield 2 g Al2O3

4 mol Al@27g/mol

3 mol O

2

@32g/mol

2 mol Al

2O3@102g/mol

108 g + 96 g = 204 gSlide3

?

Visualizing a Chemical Reaction

Na + Cl

2

NaCl

___ mole Cl

2

___ mole NaCl

___ mole Na

2

10

5

10

2

10

5

10Slide4

Types of Chemical Reactions

Synthesis

(combination) reaction

Decomposition

reaction

A

Single-replacement

reaction

BDouble-replacement reactionCombustion reaction (of a hydrocarbon)

A + B

 ABAB  A + B

A + BC

 AC + B

AB + CD

 AD + CB

C

xHy + O2  CO2 + H2O

A

use activity series to predict products/reactivity

B

use solubility chart to predict products/reactivity

element

compound

element

compound

All compounds…Slide5

Practice: Balance and Classify

Ca

(OH)

2

+ HCl  CaCl2 + H2O ________________________ C2H4 + O2  CO2 + H2O ________________________ N2 + O2  N2O ________________________

SrCO3 

SrO + CO2 ________________________ NaI + Br2  NaBr + I2 ________________________ C2H4O + O2  CO2

+ H2O ________________________ MgBr2 + (NH4)2SO3  MgSO3 + NH4Br ________________________ AgClO3 + (NH4)2

Cr2O7  Ag2Cr2O7 + NH4ClO3______________________ Cs + H2O 

CsOH + H2 ________________________ Fe + O2  Fe3O4 ________________________Slide6

Symbols Used in Chemical Equations

“Yields”; indicates result of reaction

Used to indicate a reversible reaction (equilibrium)

A reactant or product in the solid state; also used to indicate a precipitate Alternative to (s), but used only to indicate a precipitate A reactant or product in the liquid state A reactant or product in an aqueous solution (dissolved in water) A reactant or product in the gaseous state

(

s

)

(

l)(aq)

(g)Slide7

Additional Symbols Used in Chemical Equations

Alternative to (g), but used only to indicate a gaseous product

Reactants are heated

Pressure at which reaction is carried out, in this case 2 atm Pressure at which reaction is carried out exceeds normal

atmospheric pressure

Temperature at which reaction is carried out, in this case 0 oC Formula of catalyst, in this case manganese (IV) oxide, used to alter the rate of the reaction

2 atm

pressure

0

oCMnO2

DSlide8

Signs of Chemical Reactions

There are five main signs that indicate a chemical reaction has taken place:

change in color

change in odor

production of new

gases or vapor

input or release

of energy

difficult to reverse

release

inputSlide9
Slide10

Combustion

O

2

General form: CxHx + O2CO2

H2O

++carbon-hydrogen compoundcarbondioxideC4

H10

+oxygen

waterCO2H2O4513/213

8102Slide11

1. Write a word equation for the reaction

Write a balanced equation for the reaction between chlorine

and solid sodium bromide to produce bromine and solid sodium chloride.

2. Write the correct formulas for all reactants and products, (with correct phases of matter)

3. Balance the resulting equation

chlorine + sodium bromide  bromine + sodium chlorideCl2(g) +

NaBr(s)  Br2

(l) + NaCl(s)Writing Equations Practice22Slide12

1) Write a word equation for the reaction

2) Write the correct formulas for all reactants and products

3) Balance the resulting equation

aluminum sulfate + calcium chloride

 calcium sulfate

Write the balanced equation for the aqueous reaction between aluminum sulfate and calcium chloride to form a white precipitate of calcium sulfate.+ aluminum chloride

?

?

Al2(SO4)3(aq) + CaCl2(aq)  CaSO4(s) + AlCl3 (

aq)332Slide13

Oxidation-Reduction Reactions

“Redox” reactions involve the

transfer of electrons (e-)

Reduction

: gain e-

Oxidation: lose e- “LEO the lion says, ‘GER’” “OIL RIG”Use oxidation states to keep track of the e-Slide14

Leo says Ger

“

L

ose electron  oxidation” Zn  2e- + Zn2+“Gain electron  reduction”2e-

+ Cu2+

 Cu

My name is Leo. Grr-rrrr…Slide15
Assigning Oxidation States

Specific rules for assigning Ox #’s

Usually the same charge assigned by the PT

H is almost always +1 O is almost always -2 F is always -1 in compounds For elements (H2, O2, F2, Ca, K, etc ) the oxidation state always = 0Some exceptions do exist!Slide16

Assigning Oxidation Numbers

Overall charge = sum of the oxidation states of all atoms in it

Neutral Compounds

(e.g. H2O, CO2, CH4)H2O : The overall charge is 2(1) + -2 = 0CO2: What is the oxidation state of C? Since C + 2 (O) = 0… C + 2(-2) = 0, thus…

CH

4: Is C still +4? H is always +1 To remain neutral… 4(1) + C = 0 C must = - 4H = +1and O = -2C = +4Slide17

Assigning Oxidation Numbers

Charged compounds

(e.g. NO

3-, CO32-) NO3- or (NO3)- : What is the oxidation # of N? O is -2, and the overall charge is -1 So N + 3(O) = -1 or N + 3(-2) = -1 N = + 5

(CO

3)2-: What is the oxidation # of C? O is -2, and the overall charge is -2 So C + 3(O) = -2 or C + 3(-2) = -2 C = +4The oxidation # of ions = charge of ions Mn3+ has an oxidation # of +3 S2- has an oxidation # of -2Slide18

Assigning Oxidation # Practice

Assign oxidation numbers to each atom

Cl2 Fe2+ ClO3- ClO4- IO2-

CrO

42- Fe3(PO4)2 CoSO4

Cl: 0

(element)Fe: 2+ (ion)O: 2-, 3(2-) + Cl = 1-…Cl: 5+O: 2-, 4(2-) + Cl = 1-…Cl: 7+O: 2-, 2(2-) + I = 1-…I: 3+O: 2-, 4(2-) + Cr = 2-…Cr: 6+Fe: 2+

(ion) PO4:3- (ion)….O:2-, 4(2-) + P = 3-, P: 5+Co: 2+ (ion) SO4:2- (ion)….O:2-, 4(2-) + S = 2-, S: 6+Slide19

Assigning Oxidation Numbers Review

Try these…MnO

4

-, Cr2O72-, C2O42-(MnO4)- O = -2, so [4(-2) + Mn = -1] Mn = +7(Cr2O

7)

2- O = -2, so [7(-2) + 2Cr = -2] 2Cr = 12, therefore… (C2O4)2- O = -2, so [2C + 4(-2) = -2] 2C = 6, therefore…Cr = +6C = +3Slide20
Oxidation-Reduction Reactions

Two separate reactions occurring simultaneously

Oxidation:

oxidation # of an atom increasese.g. Fe(s) → Fe3+(aq)Reduction: oxidation # of an atom is “reduced”e.g. O2(g) → O2-(aq)When occurring together…Fe(s) + O2(g) → Fe3+(aq

) + O2-(

aq)This is the redox reaction responsible for rust!But, how do we balance this?(ox # goes from 0 → +3)(oxidation # goes from 0 → -2)Slide21

Balancing by Half-Reactions*in acidic solution

Assign oxidation states for each element.

Write separate half-reactions for the reduction/oxidation reactions.

Balance all the atoms EXCEPT O and H.

Balance the oxygen with water (H

2O).Balance the hydrogen with hydrogen ions (H+).Balance the charge with electrons.Multiply each half-reaction by an appropriate number to make the electrons equal.Combine both reactions into one and cancel the e - Slide22

Balancing by Half-Reactions*in acidic solution

CH

3OH (aq) + Cr2O72-(aq) → CH2O(aq) + Cr3+(aq)1. Assign oxidation states. C

-2H

4+O2- + (Cr26+O72-)2- → C0H2+O2- + Cr3+2. Write separate half-reactions for the reduction and oxidation reactions. (only keep charges that are changing…)Ox: C-2H4O → C0H2O (C is going from -2 to 0)

Red: (Cr26+O

7)2- → Cr3+ (Cr is being reduced from +6 to +3) Slide23

3.

For each half reaction, balance all atoms EXCEPT O and H.

Balance the oxygen by adding water (H

2O).Balance the hydrogen by adding hydrogen ions (H+)Balance the charge by adding electrons.…use the oxidation state as a guideMultiply each half-reaction by an appropriate number to make the electrons equal.Add the reactions together and cancel e-/simplify.

Balancing the half reactions…

+ 2H+ + 2e-Ox: C2-H4

O → C0

H2ORed: (Cr26+O7)2- → Cr3+2

+ 7H2O14H+ +6e- +3 (

)3CH4O → 3CH2O + 6H+ + 6e-

3 CH

4

O

+ + Cr2O7

2- → 3 CH2O + 2 Cr3+ + 7 H2O8 H

+Red: (Cr2

6+O7)2- → Cr3+Slide24

Ox:

C

2-

H4O → C0H2O 3. For each half reaction, balance all the atoms EXCEPT O and H. 4. Balance the oxygen by adding water (H2O).Balance the hydrogen by adding hydrogen ions (H

+)

Balance the charge by adding electrons.…use the oxidation state as a guideBalancing the Oxidation…Carbon is already balanced!

+ 2H+

+ 2e-Oxygen is already balanced!Slide25

On to the reduction…

(Cr26+O7)2- → Cr3+Balance all elements except H and O Balance O by adding H2O, if necessaryBalance H by adding H+,if necessary

Balance charge by adding e-

Remember, you only care about the charges that are changing… 2+ 7H2O14H+ +

6e- +Slide26

Adding Half-Reactions*in acidic solution

Now add the two reactions together…

Ox: CH4O → CH2O + 2H+ + 2e-Red: 6e- + 14H+

+ Cr2O

72- → 2Cr3+ + 7H2O7. Multiply each half-reaction by an appropriate number to make the electrons equal. CH4O → CH2O + 2H+ + 2e- 6e- + 14H+ + Cr2O72- → 2Cr3+ + 7H2O 3CH4O → 3CH2O + 6H+ + 6e-

3 (

)Slide27

6e- + 14H+ + Cr

2

O

72- → 2Cr3+ + 7H2O 3CH4O → 3CH2O + 6H+ + 6e- 3CH4O + + Cr2O7

2- → 3CH

2O + 2Cr3+ + 7H2O …and the reaction is now balanced!

8H

+Adding Half-Reactions*in acidic solution

8. Add the reactions together and cancel e-/simplify.Slide28

Practice Balancing Redox Reactions

Unbalanced reaction (in acid):

MnO

4 + Fe2+  Mn2+ + Fe3+Balanced Reduction half-reaction:8H+ + MnO4 + 5e  Mn2+ + 4H

2O

Balanced Oxidation half-reaction: Fe2+  Fe3+ + eBalanced overall reaction:8H+ + MnO4 + 5Fe2+  Mn2+ + 5Fe3+ + 4H2O5(

)Slide29

Balancing by Half-Reactions

*in basic solution

Assign oxidation states.

Write separate half-reactions for the reduction/oxidation reactions.

Balance all the atoms EXCEPT O and H.

Balance the oxygen by adding water (H2O).Balance the hydrogen by adding H+.Balance the charge by adding electrons.Multiply each half-reaction by an appropriate number to make the electrons equal.Combine both reactions into one and cancel.Add OH- to both sides to cancel out H+ and create H2O. Simplify further, if necessary.Slide30

Balancing by Half-Reactions(in basic solution)

Let’s balance a previous example in basic solution

Remember, it is all the same steps up to this point

3CH4O + 8H+ + Cr2O72- → 3CH2O + 2Cr3+ + 7H2O3CH4O + + Cr2O72- → 3CH2

O + 2Cr3+ + 7H2

O + 8OH-3CH4O + H2O + Cr2O72- → 3CH2O + 2Cr3+ + 8OH-+ 8OH-

+ 8OH-

8H2OSlide31

Practice Balancing Basic Redox Rxns

Unbalanced reaction:

ClO

 + Zn  Cl- + Zn2+Balanced Reduction half-reaction:2e- + 2H+ + ClO-  Cl

- + H2O

Balanced Oxidation half-reaction: Zn  Zn2+ + 2e- Balanced overall reaction (acidic):2H+ + ClO + Zn  Zn2+ + Cl- + H2OBalanced overall reaction (basic):

H2O + ClO

 + Zn  Zn2+ + Cl- + 2OH-Slide32

Ca

Activity SeriesFoiled again:Aluminum is knocked out by Calcium

Element Reactivity

Li

Rb

KBaCaNaMgAlMnZnCrFeNiSnPbH2CuHgAgPtAu

Halogen Reactivity

F2Cl2Br2I2

PrintableVersionofActivitySeriesSlide33

Mg + AlCl

3

Al + MgCl

2

Predict if these reactions will occur…

Al + MgCl

2

Can magnesium replace aluminum?

Activity Series

YES, magnesium is more reactive than aluminum.

2

2

3

3

Can aluminum replace magnesium?

NO,

aluminum is less reactive than magnesium.

Therefore,

no reaction

will occur.

NR (No Reaction)

MgCl

2

+ Al

No reaction

We must determine if the lone element is more reactive than the bonded one… metals replace metals or non-metals replace nonmetals

Order of reactants

DOES NOT

determine how

they react.Slide34

More SR Reactions…

FeCl

2

+ Cu MgBr2 + Cl2

“Magic blue-earth”

Zinc in nitric acid

2

A + BC

AC + B

General Form

Zn(NO

3

)

2 + H2

Can Fe replace Cu?

Yes

Li

Rb

K

Ba

Ca

Na

Mg

Al

Mn

Zn

Cr

Fe

Ni

Sn

Pb

H

2

Cu

Hg

Ag

Pt

Au

F

2

Cl

2

Br

2

I

2

Can

Zn

replace

H?

Yes

Can

Br

replace

Cl?

No

NO REACTION

Fe + CuCl

2

Zn + HNO

3

MgCl

2

+ Br

2

Activity SeriesSlide35

Double Replacement Reactions

K

2

CO

3

(aq)Potassium carbonateBaCl2

(aq)Barium chloride

2 KCl (aq)Potassium chloride

BaCO3 (s)Barium carbonate

+

+Slide36

Formation of a solid precipitate:

AgNO

3

(aq) + KCl(aq)

 KNO

3 (aq) + AgCl(s)Slide37

TABLE OF SOLUBILITIES IN WATER

aluminum

ss

s

n

s

n

i

s

s

i

s

d

ammonium

s

s

s

s

s

s

s

s

s

s

s

barium

s

s

i

s

i

s

s

s

i

i

d

calcium

s

s

i

s

s

ss

s

s

i

ss

d

copper (II)

s

s

i

s

i

i

n

s

i

s

i

iron (II)

s

s

i

s

n

i

s

s

i

s

i

iron (III)

s

s

n

s

i

i

n

s

i

ss

d

lead

s

ss

i

ss

i

i

ss

s

i

i

i

magnesium

s

s

i

s

s

i

s

s

i

s

d

mercury (I)

ss

i

i

i

ss

n

i

s

i

ss

i

mercury (II)

s

ss

i

s

ss

i

i

s

i

d

i

potassium

s

s

s

s

s

s

s

s

s

s

s

silver

ss

i

i

i

ss

n

i

s

i

ss

i

sodium

s

s

s

s

s

s

s

s

s

s

s

zinc

s

s

i

s

s

i

s

s

i

s

i

acetate

bromide

carbonate

chloride

chromate

hydroxide

iodide

nitrate

phosphate

sulfate

sulfide

i = insoluble

ss = slightly soluble

s = soluble

d = decomposes

n = not isolated

SOLID

SOLID

AQUEOUS

LegendSlide38

Solubility Rules

1. Most nitrates are soluble.

Most salts containing Group I ion and ammonium ion, NH

4

+

, are soluble.

Most chloride, bromide, and iodide salts are soluble, except Ag

+, Pb2+ and Hg22+.Ohn-Sabatello, Morlan, Knoespel,

Fast Track to a 5 Preparing for the AP Chemistry Examination 2006, page 914. Most sulfate salts are soluble, except BaSO4, PbSO4, Hg2

SO4, and CaSO4.

Most hydroxides except Group 1 and Ba(OH)2, Sr(OH)2, and Ca(OH)2 are only slightly soluble.

Most sulfides, carbonates, chromates, and phosphates are only slightly soluble.Slide39

FeCO

3

Na

+

Fe

2+iron (II) chloride + sodium carbonate

Cl

2

Using the SOLUBILITY TABLE:sodium chloride is soluble iron (II) carbonate is insoluble

CO3

Fe2+FeNa+Na2

Cl

-

CO

3

2-

Cl-

CO

3

2-

NaCl

sodium chloride

iron (II) carbonate

+

(aq)

(s)

2

FeCl

2

Na

2

CO

3

NaCl

FeCO

3

(aq)

(s)

+

+

Predict if a reaction will occur when you combine aqueous solutions of iron (II) chloride and sodium carbonate…

If the reaction does occur, write a balanced chemical equation showing it (be sure to include phase notation).

(aq)

(aq)

Balanced chemical equationSlide40

KNO

3

Na

+

K

+potassium chloride + sodium nitrate

KCl

(aq)

Using the SOLUBILITY TABLE:sodium chloride is soluble potassium nitrate is soluble

NaNO3 (aq)

K+Na+

Cl

-

NO

3-

Cl-

NO3-

NaCl

sodium chloride

potassium nitrate

+

(aq)

(aq)

Predict if a reaction will occur when you combine aqueous solutions of potassium chloride and sodium nitrate…

If the reaction does occur, write a balanced chemical equation showing it (be sure to include phase notation).

Notice that nothing has really changed because the ions are still dissolved in water!

NRSlide41

Pb

2+

NO

3

–

Na

+

CI

–

Ions in Aqueous Solution Expt.

Pb(NO

3

)

2

(s)Pb(NO3)

2(aq)Pb2+(aq) + 2 NO3–(aq)add

waterNaCI(s) + H2O(l)

Dissociation reactions

: solids mixed with water dissociate into ions

+ H

2

O(l)

Na

+

(aq) + CI

–

(aq)

Mix them and get…

Balance to get

complete ionic equation

…

Cancel

spectator ions

to get

net ionic equation

…

NaCI

(

aq

)

NO

3

–

Pb

2+

NO

3

–

NO

3

–

in solution,

aqueous,

soluble,

dissolved

Na

+

CI

–

Chem

ThinkSlide42

Mix them and get…

Pb

2+

(aq) + 2 NO31–(aq)

+ 2 Na

1+(aq) + 2 CI–(aq)PbCI2(s) + 2 NO31–(aq) + 2 Na

1+(aq)

Pb2+(aq) + 2 CI–(aq)

PbCI2(s)Pb(NO3)2(aq) + NaCI(aq)

Balance to get complete ionic equation…separate anything (aq)

Cancel spectator ions to get net ionic equation…

Solubility

Chart

Solid (precipitate)

in solution

(aqueous)

Pb

2+

NO

3

–

Na

+

CI

–

NO

3

–

Na

+

CI

–

Pb

2+

NO

3

–

Na

+

CI

–

NO

3

–

Na

+

CI

–

PbCI

2

+ NaNO

3

(s)

(aq)

2

2Slide43

Pre-lab:

1.

What ions are present in the following solutions?

NaCl(aq)  ____________________ AgNO3(

aq

)  ____________________When these solutions are mixed together, a precipitate is seen. What are the new combinations of ions that could have formed the precipitate? ____________________ and ____________________Using the solubility table, which new combination will form a precipitate? ____________________ Which new combination will remain in solution? ____________________

5. Write the complete ionic equation

for this reaction. Be sure to indicate the correct phase (reaction condition) for each reactant and each product.6. Write the net ionic equation for this reaction by canceling out spectators. Again, include the phases (reaction conditions).7. Explain why you would expect no reaction between solutions of KOH(aq) and NaOH(aq).

Na+(aq)

Cl-(

aq)Ag+(

aq)

NO

3

-(aq)

Na+(aq)

Cl-(aq)

Ag

+

(

aq

)

NO

3

-

(

aq

)

Cl

-

(

aq

)

Ag

+

(

aq

)

Na

+

(

aq

)

NO

3

-

(

aq

)

AgCl(

s

)

Na

+

(

aq

)

+ Cl

-

(

aq

)

+ Ag

+

(

aq

)

+ NO

3

-

(

aq

)

+ Na

+

(

aq

)

+ NO

3

-

(

aq

)

AgCl(

s

)

+

Cl

-

(

aq

)

Ag

+

(

aq

)

AgCl(

s

)

When the cations switch places they end with a hydroxide

(no new combination is formed)Slide44

Ba

2+

OH

–

OH

–

NO

3

–

NO

3

–

Mix together Zn(NO

3

)

2

(aq) and Ba(OH)

2

(aq):

Zn

2+

(aq) + 2 NO

3

–

(aq)

Ba

2+

(aq) + 2 OH

–

(aq)

Ba(OH)

2

(aq)

Zn(NO

3

)

2

(aq)

Balance to get

complete

ionic equation

…

Zn

2+

Zn(NO

3

)

2

(aq) + Ba(OH)

2

(aq)

Zn(OH)

2

(s) +

Ba(NO

3

)

2

(

aq

)

Zn

2+

(aq) + 2 NO

3

–

(aq)

+ Ba

2+

(aq) + 2OH

–

(aq)

Zn(OH)

2

(s) + 2 NO

3

–

(aq)

+ Ba

2+

(aq)

Mix them and get…

Zn

2+

(aq) + 2 OH

–

(aq)

Zn(OH)

2

(s)

Cancel

spectator ions

to get

net ionic equation

…

Solubility

ChartSlide45

Separation of Cations

You have a solution containing Fe

2+

, Cu2+, Ba2+, Ag+ and K+ ions. By what means could you separate these ions from each other?In Chem I, we discussed various ways to separate things…DistillationFiltrationCentrifugationReactivity

Will any of these work to separate aqueous ions?Slide46

Separation of Cations

Fe

2+

, Cu2+, Ba2+, Ag+, K+ (aq) + Cl- (aq)

AgCl

(s)Fe2+, Cu2+, Ba2+, K+ (aq)

BaSO

4(s)Fe2+, Cu2+, K+ (aq)

CuCrO4(s)Fe2+, K+ (aq)

+ SO42- (aq) + CrO42- (aq)

FeS

, Fe

3

(PO

4)2 , Fe(OH)2 , or FeCO

3(s)K+(aq) + S2-, PO43- OH- or CO32- (aq)

Slide47

Separation of Cations

Pb

2+

, Ca2+, Zn2+, NH4+ (aq) + CrO42-(aq

)

PbCrO4 (s)Ca2+, Zn2+, NH4+ (aq)

C

aSO4(s)Zn2+, NH4+ (aq)

NH4+ (aq)

+ SO42- (aq)

ZnCO3, Zn3(PO4)2 , Zn(OH)

2

, or ZnS(s)

+ CO

32-, PO43- OH- or S2- (aq)

Try this example on your own… Slide48

Summary of Classes of Reactions

Chemical reactions

Double Replacement

reactionsAcid-BaseReactions

Oxidation-Reduction

ReactionsCombustion Reactions

Single Replacement

reactions Synthesis and Decomposition reactions