I Chemical Reactions One Or More Substances Are Changed Into One Or More New

Chemistry

Chapter 9 Chemical Reactions

I Chemical Reactions – one or more substances are changed into one or more new

substances

A. Reactants ------> Products

( ------> “yields”)

B. Word Equation

Ex. Iron and oxygen yield iron(III) oxide

II Chemical equations – formulas are used to explain what occurred.

A. Skeleton Equation – does NOT indicate amounts of the reactants (NOT Balanced)

Fe(s) + O2 (g) ---- > Fe2O3 (s)

B. The physical state of each substance is indicated by:

1. (s) = solid

2. (g) = gas

3. (l) = liquid

4. (aq) = aqueous

C. Catalysts – a substance that speeds up or slows down a reaction without being used up is written above or below the arrow

MnO2

H2O2 (aq) ------> H2O(l) + O2 (g)

D. When heat is required, the symbols H or ∆H, or the word “heat” is written above or below the arrow.

∆H

KClO3 (s) ------> KCl(s) + O2 (g)

III Balancing Chemical Equations

A. Law of Conservation of Mass

B. In EVERY balanced equation, each side of the equation must have the same number of atoms of each element.

C. Rules of Balancing

1. Determine the correct formulas for all reactants & products.

2. Reactants on left

Products on right.

Arrow in between

3. Balance the equation, one element at a time, using coefficients.

4. Polyatomic ions appearing unchanged on both sides count as a single unit.

5. Make sure coefficients are in the lowest ratio.

IV Types of Chemical Reactions

A. Combination/Synthesis – two or more substances react to form a complex substance.

Ex. A + B ------> AB

_____ Fe + _____ S ------> Fe2S3

B. Decomposition – a complex substance is broken down to simple substances.

Ex. AB ------> A + B

______H2O ------> _____ H2 + _____ O2

C. Single Replacement – an element replaces an element in a compound.

1. (Cationic) Metals

AB + C ------> CB + A

_____ AgNO3 + Cu ------> Cu(NO3)2 + _____ Ag

2. (Anionic) Nonmetals

AB + C ------> AC + B

_____ KI + _____ Cl2 ------> _____ KCl + _____ I2

D. Double Replacement – two ionic compounds switch ions forming two different

ionic compounds.

AB + CD ------> AD + CB

_____NaOH + _____ CuSO4 ------> _____ Na2SO4 + ____ Cu(OH)2

E. Combustion – an element or compound ** reacts with oxygen “often” producing

heat or light

** Hydrocarbons will produce CO2 + H2O

IF it is complete combustion

Ex. X + O2 ------> XO + E↑

_____ Mg + _____ O2 ------> _____ MgO + E↑

CxHy + O2 ------> CO2 + H2O + E↑

_____ C8H18 + _____ O2 ------> _____ CO2 + _____ H2O + E↑

V Types:

Synthesis (Combination) reaction – two or more simple substances react to

form a complex product.

A. Group A Metal & a Nonmetal

1. Bring over one of each atom

2. Check charges to obtain the formula

3. Balance the equation

+1 -1

Ex. _____ Na + ____ Cl2 ------> ____ NaCl

B. Nonmetal Oxides and water react to produce an acid.

Ex. SO3 + H2O ------> _____ H2SO4

C. Metallic oxides and water react to produce a base. Base = (-OH group)

+2 -1

Ex. CaO + H2O ------> Ca(OH)2

**D. Two nonmetals react, more than one product is possible

S + O2 ------> SO2

____ S + ____ O2 ------> ____ SO3

VI Decomposition Reactions –a complex substance is broken down to simpler

substances. (Most require energy to occur.) The products can be any

combination of elements +/or compounds. Simple binary compounds will break

down to the elements.

A. Steps:

1. Break the compounds into the elements.

2. Check the diatomic list.

3. Balance the equation.

Ex. _____ H2O(l) ------> _____ H2(g) + _____ O2 (g)

MnO2

*** _____ H2O2 (aq) ------à _____ H2O(l) + _____ O2(g)

VII Single Replacement Reactions – an element will replace an element in a

compound.

A. Metal Displacement/Cationic – reactive metal will replace any metal listed below

it on the activity series. (See Diagram)

+2 -1

_____ Cu (II) + _____ AgNO3(aq) ------> _____ Ag + _____ Cu(NO3)2

_____ Mg + Ca(NO3)2 ------> No Reaction (NR)

B. Nonmetal Displacement/Anionic - a nonmetal will replace a nonmetal. This is usually limited to the halogens. Halogen activity decreases as you move down the family.

_____ Cl2 + _____ KI ------> _____ I2 + _____ KCl

C. Steps:

1. Like bumps out like.

2. Check the charges for the new compound

3. Check the diatomic list for the free element.

4. Balance the equation

D. Metal with an acid - the metal will bump H2 (g) as a product. (Lab)

+1 -1 +2 -1

Ex. _____ Mg + _____ HCl ------> _____ H2 + _____ MgCl2

E. Metal with water will produce a base and release H2(g)

+2 -1

Ex. _____ Ca + _____ H2O ------> _____ H2 + _____ Ca(OH)2

HOH

VIII Double Replacement Reactions – two ionic compounds switch ions to form two

NEW ionic compounds.

A. Steps:

1. Switch ions, bring over 1 of each.

2. Check charges to obtain new formula

3. Balance the equation.

+2 -1 +1 -1 +2 -1 +1 -1

Ex. Pb(NO3)2 + _____ KI ------> ______PbI2 + ____ KNO3

B. Double Replacement involving an acid and a base result in water and an ionic salt forming.

+1 -1 +1 -1 +1 -1 +1 -1

Ex. HCl + NaOH ------> HOH + NaCl

*** Reactions will go to completion if one or more of the following is produced:

1. a precipitate/insoluble solid (See Chart)

2. a gas (See Chart)

3. water

IX Combustion Reactions : an element or compound reacts with O2 often producing

heat or light.

A. Element and O2 - see synthesis

B. Hydrocarbon and O2

1. Complete combustion the products are CO2 + H2O

2. Incomplete combustion will also produce elemental carbon & CO (yellow flame)

Ex. _____CH4 + _____O2 ------> _____ CO2 + _____H2O

*** Completion – on previous screen