chemical reactions chapter 8 evidence of a chemical rx 1. color change 2. formation of a gas 3. heat...

CHEMICAL CHEMICAL REACTIONSREACTIONS

CHAPTER 8CHAPTER 8

Evidence of a Chemical Evidence of a Chemical RxRx

1.  Color change2.  Formation of a gas3.  Heat produced or heat

absorbed4.  Formation of a precipitate

5. New odor 6. Production of light

I. I. CHEMICAL EQUATIONSCHEMICAL EQUATIONS DefinedDefined

1.Are a condensed statement of facts about a chemical reaction 2Na + Cl2 2NaCl

I.I. CHEMICAL EQUATIONSCHEMICAL EQUATIONS

2.Represent the changes in BONDINGBONDING and ENERGYENERGY that take place in a reaction

2Na + Cl2 2NaCl

A. A. DefinedDefined

II. II. Information in an Information in an Equation Equation

A.A.Reactants:Reactants: 1.are all substances

that exist the reaction

2.are always located to the

2Na + Cl2 2NaCl

before

left of the arrow

II. II. Information in an Information in an Equation Equation

B.B. Products:Products: 1.are all substances

that exist the reaction

2.are always located to the

2Na + 1Cl2 2NaCl

after

right of the arrowright of the arrow

II. II. Information in an Information in an Equation Equation

C.C.Arrows:Arrows: 1.Horizontal Arrows

Stand for or

2Na + 1Cl2 2NaCl

yields

produces

II. II. Information in an Information in an Equation Equation

C.C.Arrows:Arrows: 2.Vertical Arrows

indicates that the substance will leave the reaction as a gas ( )

HCl + Zn H2 + ZnCl2

effervescence

II. II. Information in an Information in an Equation Equation

C.C.Arrows:Arrows: 2.Vertical Arrows

indicates that the substance settles to the bottom of the solution as a solid

AgNO3 + Zn Ag + Zn(NO3)2

( is formed)precipitate

II. II. Information in an Information in an Equation Equation

D. Showing Phase:D. Showing Phase: ( ) gas

( ) liquid ( ) solid

( ) dissolved in H2O

H2(g) + O2(g) H2O(l)

g

ls

aq

E. Coefficients:E. Coefficients: 1.are whole #’s written in front of

formulas2.indicate the ratio of each cmpd

in the equation3.are used in balanced eq.to

make the # atoms of each element on the reactant side = # atoms of each element on the product side

22H2(g) + 11O2(g) 22H2O(l)

Writing Equations 1. Use chemical formulas2. Rules – write Reactants Products.

3. Balancing equations using Coefficient –

Coefficient - is the smallest whole # that appears in front of a formula

Symbols : + And Yield (l) Liquid Gaseous product ppt Delta Reversible rxn (g) gas(s) Solid (aq) aqueous

F. Showing Energy Changes:F. Showing Energy Changes: 1.

• Absorb energy• Have + energy on reactant side

2. • Release energy• Have + energy on product side

2H2(g)+ 11O2(g)+ energyenergy 2H2O(l)

Endothermic Rxn

Exothermic Rxn

Catalyst –

is a substance that changes the rate of a chemical reaction, but can be recovered unchanged.

Reversible reaction –

is a chemical reaction in which the products reform the original reactants.

III. III. Balanced Equations Balanced Equations

1.States:

A. Obey the Law of A. Obey the Law of Conservation of MatterConservation of Matter

Matter cannot be created or destroyed

2.Thusthe number of atoms of each element on the reactant side

of the equation. must the number of atoms of each

element on the product side of the equation.

III. III. Balanced Equations Balanced Equations (not in (not in

notes)notes) A. Obey the Law of A. Obey the Law of Conservation of MatterConservation of Matter

equal

3.Since

the number of atoms is conserved so is the mass.

If you started with 10 grams of reactants, there will be 10 grams of products.

III. III. Balanced Equations Balanced Equations A. Obey the Law of A. Obey the Law of Conservation of MatterConservation of Matter

III. III. Balanced Equations Balanced Equations B.B.Background:Background:

1.1. all atoms must be accounted all atoms must be accounted forfor

2.2.Use Use to to make the total make the total number number of atoms of each of atoms of each element in the element in the reactants equal the reactants equal the total number of total number of atoms of each atoms of each element in the element in the productsproducts.

III. III. Balanced Equations Balanced Equations B.B.Background:Background:

coefficients

III. III. Balanced Equations Balanced Equations

B.B.Background:Background:

3.3. NeverNever change subscripts! change subscripts!

4.4.If an element occurs If an element occurs more than once on more than once on one side of the one side of the equation it is usually equation it is usually (but not always) best (but not always) best to balance it last.to balance it last.

B. CoefficientsB. Coefficients

1.Are numbers that indicate how many atoms or molecules of each substance are involved in the reaction

2.Are written in of formulas

3.Are used to balance an eq.

22AlCl3whole

front

III. III. Balancing Equations Balancing Equations C. General Rules for Balancing C. General Rules for Balancing

Eq.Eq. 1.Write the equations and 1.Write the equations and

balance them inbalance them in2.Count the number of atoms of 2.Count the number of atoms of

each element in the reactants each element in the reactants and products. and products.

3. B3. Balance the elements one at a alance the elements one at a time by using coefficients. time by using coefficients.

Never change subscripts!Never change subscripts!

pencil

III. III. Balancing Equations Balancing Equations D. Steps to Balancing an Eq.D. Steps to Balancing an Eq.

2. Balance metals2. Balance metals3. Balance nonmetals3. Balance nonmetals4. Balance oxygen4. Balance oxygen5. Balance hydrogen5. Balance hydrogen6. Recount all atoms6. Recount all atoms7. If 7. If everyevery coefficient will coefficient will

reduce, rewrite in the simplest reduce, rewrite in the simplest whole-number ratio.whole-number ratio.

III. III. Balancing Equations Balancing Equations E. Sample ProblemsE. Sample Problems

ClCl22 + NaBr + NaBr Br Br22 + NaCl + NaCl

AlAl22(SO(SO44))33 + CaCl + CaCl22 AlCl AlCl33 + CaSO + CaSO44

III. III. Balancing Equations Balancing Equations

D. Steps to Balancing an Eq.D. Steps to Balancing an Eq. 1. Check for Diatomic 1. Check for Diatomic

moleculesmolecules

if these elements never appear by themselves in an equation, they must be written with the subscript 2

H2 N2 O2 F2 Cl2 Br2 I2

IV. IV. Types of Reactions Types of Reactions

A. Synthesis Reaction• Two or more substances combine to form • a new compound.

It follows this general equation:Element + Element compd.

A + X AX

Mg + O2 +2 -2

2 2 MgO

A. Synthesis - Practice Problems

1. H + O H2O

Remember diatomic molecules:

H, N, O, F, Cl, Br, I (Super 7)

2. S + O SO

2 2 2 2

22 2S - 1 1O - 2 1

22

2

IV. IV. Types of Reactions Types of Reactions

3.Co + F

4. Na + F

5.U + F

2

+3 -1

CoF3

+1 -1

2NaFNa -1 1F - 2 1

22

2

2

2

2

+6 -1

UF6

U – 1 1F – 2 6

3

6

A. Synthesis - Practice ProblemsIV. IV. Types of Reactions Types of Reactions

A single compound undergoes a reaction that produces two or more simpler substances.

AX A + X

Compound element + element

2 HgO 2 Hg + O2

2H2O 2H2 + O2

A. DecompositionIV. IV. Types of Reactions Types of Reactions

Practice Problems1. H + Cl 2. NaBr 3. FeCl3 4. Ba + N

IV. IV. Types of Reactions Types of Reactions

C. Single Replacement Reactions

One element replaces a similar element in a compound.

A + B X A X + B

Al + Fe (NO3)2 Fe + Al (NO3)3 2 3 3 2

IV. IV. Types of Reactions Types of Reactions

Activity Series Is a list of elements organized according to

the ease with which they undergo certain chemical reactions.

The elements on top are said to be more active than the elements below them. Elements on top can replace the elements below them.

Li, Rb, K, Ba, Sr, Ca, Na, Mg, Al, Mn

F2, Cl2, Br2, I2

IV. IV. Types of Reactions Types of Reactions

Practice!!!

Will copper replace silver in silver nitrate?

Mg + CuSO4 +2 +2 -2

Cu + MgSO4

Magnesium and Copper switch places ! Like replaces like!

Cu + AgNO3

Will this rxn occur?

+2 +1 -1 Ag + Cu(NO3)2

Cu – 1 1Ag - 1 1NO3- 1 2

2

22

2

2

YES!

D. Double Replacement

KI + Cu(NO3)2

+1 -1 +2 -1 KNO3 + CuI2

K – 1 1I – 1 2Cu – 1 1NO3-2 1

2

2

2

2

22

IV. IV. Types of Reactions Types of Reactions

Solubility – The amount of a substance that is dissolved at solution

equilibrum in a specific amount of solvent at a specified temperature.

Solubility is affected by: 1.Surface area2.Agitating solution3.Heating a solvent – increases

collisions

Immiscible = Substances that are not soluble in each other

Miscible = are soluble in each other.

Solubility Rules1.All Nitrates compd. are soluble

2. All Grp I & NH4 compds are soluble

6. All S –2, PO4 –3, CO3 –2 compd are NOT SOLUBLE

3. All Chlorine compd are soluble EXCEPT: AgCl, PbCl2, Hg2Cl2

4. All Sulfate compd are soluble EXCEPT: BaSO4, CaSO4, PbSO4

5.All OH compds are NOT SOLUBLE Except: Grp I & half of IIA

Combustion Reactions

Kaboom!!

A substance that combines with oxygen, releasing a large amount of energy in the form of light and heat.

Combustion rxns Hydrocarbon + Oxygen Carbon dioxide & Water

CxHy+ O2 CO2 + H2O

PracticeCH4 + O2 CO2 + H2O 2 2

C 1 1H 4 2O 2 34

44