I II III IV V

I. Intro to Reactions

Ch. 9 – Chemical Reactions

BACKGROUND

chemical reaction: process in which 1 or more substances are changed into 1 or more different substances.

chemical equation: uses symbols and formulas to represent the identities and relative amounts of reactants and products in a chemical reaction

A.Signs of a Chemical Reaction Evolution of heat and light Formation of a gas Formation of a precipitate

· precipitate: solid produced as result of chemical rxn in a soln. and separates from the soln.

Color change

CHEMICAL EQUATIONS

Three requirements for chemical equations:

· a. Equation must represent known facts: actual compounds and actual lab results

CHEMICAL EQUATIONS

· b. The equation must contain correct formulas for reactants and products

- ex: diatomic elements (7)H2, N2, O2, F2, Cl2, Br2, I2

CHEMICAL REACTIONSc. Law of Conservation of Mass must be

satisfied· mass is neither created nor destroyed in

a chemical reaction

4 H

2 O

4 H

2 O4 g 32 g

36 g

· total mass stays the same· atoms can only rearrange

C. Chemical Equations

A+B C+DREACTANTS PRODUCTS word equation: (def) reactants and products represented by words

hydrogen + oxygen water

formula equation: (def) represents reactants and products of a chemical equation by their symbols or formulas

2H2 + O2 2H2O

symbols in chemical equations

symbol meaning

(s) solid state, or precipitate

↓ precipitate

(l) liquid state

(g) gaseous state

↑ gaseous state, only products

(aq) aqueous soln; dissolved in water

symbols in chemical equations

→ yields, produces

↔ reversible reaction

reactants heated

pressure conditions of rxn

higher P than normal atmospheric P

temperature of rxn.

formula of catalyst used to change speed of reaction

atm2

pressure

C0

2MnO

Reversible Reaction

reversible reaction: the products re-form the original reactants

Reversible Reaction

Oscillating Reaction

Significance of Chemical Eqn. Coefficients show relative amounts of

reactants and products 2H2 + O2 2H2O

2 molecule H2: 1 molecule O2: 2 molecules H2O

Significance of Chemical Eqn.

Relative amounts of reactants and products can be determined from reaction coefficients.

H2 + Cl2 2HCl1 molecule H2: 1 molecule Cl2: 2 molecules HCl1 mol H2: 1 mol Cl2: 2 mol HCl2.02 g H2: 70.9 g Cl2: 72.92 g HCl

I II III IV V

II. Balancing Equations

(p. 250-254)

Ch. 8 – Chemical Reactions

A. Balancing Steps

1. Write the unbalanced equation.

2. Count atoms on each side.

3. Add coefficients to make #s equal.

Coefficient subscript = # of atoms

4. Reduce coefficients to lowest possible ratio, if necessary.

5. Double check atom balance!!!

B. Helpful Tips

Balance one element at a time. Update ALL atom counts after adding

a coefficient. If an element appears more than

once per side, balance it last. Balance polyatomic ions as single

units.· “1 SO4” instead of “1 S” and “4 O”

Al + CuCl2 Cu + AlCl3

Al

Cu

Cl

1 1

1 1

2 3

2

3

6

3

33 2

C. Balancing ExampleAluminum and copper(II) chloride react to form copper and aluminum chloride.

2

2

6

I II III IV V

II. Balancing Equations

Chemical Reactions

A. Balancing Steps

1. Write the unbalanced equation.

2. Count atoms on each side.

3. Add coefficients to make #s equal.

Coefficient subscript = # of atoms

4. Reduce coefficients to lowest possible ratio, if necessary.

5. Double check atom balance!!!

B. Helpful Tips

Balance one element at a time. Update ALL atom counts after adding

a coefficient. If an element appears more than

once per side, balance it last. Balance polyatomic ions as single

units.· “1 SO4” instead of “1 S” and “4 O”

Al + CuCl2 Cu + AlCl3

Al

Cu

Cl

1 1

1 1

2 3

2

3

6

3

33 2

C. Balancing ExampleAluminum and copper(II) chloride react to form copper and aluminum chloride.

2

2

6

I II III IV V

Ch. 9 – Chemical Reactions

III. Types of Chemical Reactions

Synthesis

the combination of 2 or more substances to form a compound

only one product

A + B AB

Synthesis

H2(g) + Cl2(g) 2 HCl(g)

Al(s)+ Cl2(g) AlCl3(s)2 3 2

Synthesis

Products:· ionic - cancel charges· covalent - hard to tell

Synthesis

Reactions with oxides· Oxides of active metals react with

water to form metal hydroxides

· Active metal: Cametal oxide: CaO

reaction: CaO + H2O Ca(OH)2

Synthesis

Examples:· Mg + O2 → · S8 + O2 → · Co + F2 → · BaO + H2O →

MgO22SO288CoF3232

Ba(OH)2

Decomposition

a compound breaks down into 2 or more simpler substances

only one reactant

AB A + B

Decomposition

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

KBr(l) K(s) + Br2(l) 2 2

Decomposition

Products:· binary - break into elements· ((others - hard to tell – various

rules))

Decomposition Products for metal carbonates

· MCO3 metal oxide + CO2

· CaCO3 CaO + CO2

Products for metal hydroxides

· NOT GROUP 1 METALS

· M(OH)x metal oxide + water

· Ca(OH)2 CaO + H2O

Decomposition Products for metal chlorates

· MClO3 metal chloride + O2

· KClO3 KCl + O2

Products for acids

· acid nonmetal oxide + water (generally)

· H2SO4 SO3 + H2O

2 32

Single Replacement

one element replaces another similar element in a compound· metal replaces metal · nonmetal replaces nonmetal

A + BC B + AC

Single Replacement

Cu(s) + 2AgNO3(aq) Cu(NO3)2(aq) + 2Ag(s)

Single Replacement Activity Series: Part of series

Li > Rb > K > Ba > Sr > Ca > Na

An element can only replace another if the free element is more reactive than the element in the compound

Li + KCl

K + LiCl LiCl + K

NR (no reaction)

Single Replacement

Replacement of metal by metal· Fe2O3 + Al Al2O3 + Fe

Replacement of H in water by a metal· Na + H2O NaOH + H2

· metal + water metal hydroxide +

hydrogen

2 2

2 2 2

Single Replacement

Replacement of hydrogen in an acid by a metal· active metal + acid

metal compound + hydrogen· Mg + HCl MgCl2 + H2

Replacement of halogens· Cl2 + NaBr NaCl + Br2

2

2 2

AB + CD AD + CBDouble Replacement

ions in two compounds “change partners”

cation of one compound combines with anion of the other

Double Replacement

Pb(NO3)2(aq) + K2CrO4(aq) PbCrO4(s) + 2KNO3(aq)

E. Double Replacement Formation of a precipitate

· 2 aqueous compounds form insoluble solid

· 2KI(aq) + Pb(NO3)2(aq) PbI2(s) +

2KNO3(aq) Formation of a gas

· 1 product bubbles out of solution· FeS(s) + 2HCl(aq)

H2S(g) + FeCl2(aq)

Double Replacement

Formation of water· HCl(aq) + NaOH(aq)

NaCl(aq) + H2O(l)

Combustion

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

the burning of any substance in O2 to produce heat

A + O2 B

Na(s)+ O2(g)

C3H8(g)+ O2(g) 5 3 4

Combustion

Products:· contain oxygen· hydrocarbons form CO2 + H2O

CO2(g)+ H2O(g)

Na2O(s) 4 2