Chemical Reactions

Section 7-1

Chemical Changes in Matter

Describing Chemical Reactions

Chemical Reaction: A well defined example of a

chemical change in which one or more substances are changed to new substances.

Chemical Reaction

Reactants ProductsYields

Reactants: The substances that are about to react.

Products: The new substances that are produced.

Conservation of Mass

The mass of the reactants

EQUALSThe mass of the products.

Conservation of Mass

Mercury(II) Oxide Oxygen + Mercury

2HgO O2 + 2Hg

10.0g 0.7g + 9.3g 10.0g

Reactants

AndCarbonOxygen

Gas

C

Reactants

+ O2

Yields

Products

Carbon Dioxide

Chemical Equation

C O2+ CO2

Chemical Equation

H2O2+ H2O22

Coefficients

A number which represents the number of units of each substance taking part in a

reaction.

Coefficients

Chemical Equations

Balanced Chemical EquationThe number of atoms of

each element is the same on both sides of the equation.

Example

Ag + H2S Ag2S+ H21 22 21 1

22

Writing Balanced Equations

Step 1: Write the equation in words.

 Magnesium plus Oxygen produces

Magnesium Oxide

Step 2: Write the chemical equation using formulas and symbols.

 

Mg + O2 MgO

Step 3: Check the equation for atom balance.

Mg + O2 MgO1 12 1

Mg + O2 MgO1 12 1

2

Step 4: Choose coefficients that balance the equation.

222

2

MINOH Method

• M - Metals • I – Polyatomic Ions (SO4)

• Page 173 in the book.

• N – Non-Metals• O – Oxygen• H - Hydrogen

MINOH Example

Na2SO4+ BaCl2 → NaCl+ BaSO4

The Mole

• The atom is too small a unit for chemist to count with, so the mole is used.

• Bakers use a dozen.

• 1 mole = 6.02X1023 atoms.

• Avogadro’s number

The Mole

• The mass of a mole is different for each element.

• Use the atomic mass for that element.

• Use the periodic table.

The Mole

• 1 mole of C

• 1mole of Na

• 1mole of O2

The Mole

H20 H2O2+2 2

2 moles 2 moles 1 mole

Homework: #7-1

Section 7-1 Worksheet

Due: 01/09/09

Synthesis Reaction

Two or more substances combine to form

another substance.

Synthesis Reaction

A + B AB

2H2 +O2 2H2O

Decomposition Reaction

One substance breaks down, or decomposes, into two or

more simpler substances.

Decomposition Reaction

AB A + B

elec.

2H2O 2H2 + O2

Single Replacement Reaction

One element replaces another element in a

compound.

Replacement Reaction

A + BC AC + B

D + BC BD + C

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

Double Replacement Reaction

Two elements replace each other in two compound.

Double-replacement Reaction

AB + CD AD + CB

AgNO3+NaCl AgCl+NaNO3

Double-Replacement Reaction

Takes place if a precipitate, water, or a gas forms when two compounds in solution

are combined.

Precipitate

An insoluble compound formed during a

displacement reaction.

Combustion Reaction

A substance reacts rapidly with oxygen.

CH4+ 2O2 CO2 + 2H20

Electron TransferReactions

Electrons are transferred from one reactant to another.

2Ca + O2 2CaO

Oxidation-Reduction

OxidationThe atom that loses electrons

undergoes oxidation.

Ca Ca2+ + 2e-

Oxidation

ReductionThe atom that gains electrons undergoes

reduction.0 + 2e- 02-

Oxidation

Homework #7-2

Section 7-2

Work sheet

Due: 01/09/08

Energy Changes in Reactions

C3H8 + O2 CO2 + H2O3 45

+ Heat

Breaking Bonds

C-C-CHH H H

HH H H

O O O2

C3H8

CO2

H2O

Forming Bonds

H O

CO O

H

Heat

Energy and Chemical Reactions

Exothermic Reaction

A chemical reaction in which

energy is released.FireExplosions

Mg +2H2O ----> Mg(OH)2+H2+Heat

MR

E

Energy and Chemical Reactions

Endothermic Reaction

A chemical reaction in which energy is absorbed.

2Al203 4Al + 302

elec.

Ice Pack

NH4N03 + H2O NH4OH + HN03Heat

Reaction Rates

Reaction rates tell you how fast the reaction is going.

Factors Affecting Reaction Rates

•Temperature•Surface Area•Stirring•Concentration•Catalyst

Energy and Chemical Reactions

Catalyst A substance that speeds up a

chemical reaction without itself being permanently changed.

Catalyst

ProteinsEnzymes that act as catalysts in a living

organism.

Energy and Chemical Reactions

InhibitorsSubstance used to combine

with one of the reactants that will keeps it from reacting.

Inhibitors

BHT and BHA Food preservatives.

Catalytic Converter

CO NO2

Hydro-carbons

Catalytic Converter

CO2

N2

CO2 + H2O

Worksheets

7-3 and 7-4

Due: 1/13/09

Test: 1/15/09

Homework: #7-3

Mid Year Exam

Tuesday - Jan 20th

8 - 9:30am

C Period – Room 291

G Period – Room 289

Full Sheet of Notes

Pencil

Review Sheet (1 Point per Sheet)

Section 7-5

Equilibrium

Equilibrium

Forward and Reverse paths of a physical or chemical

change take place at the same rate.

Physical Equilibrium

A state in which the forward and reverse paths of a

physical or chemical change take place at the same rate.

H20(l) H20(g)

Chemical Equilibrium

Forward and Reverse paths of a chemical change take place at the same rate.

Reversible Reaction

Conversion of Reactants into Products and the conversion of

Products into Reactants happens at the same time .

2SO2+02 2SO3

Reversible Reaction

At the completion of a chemical reaction, a chemical equilibrium is

reached

Factors Affecting Chemical Equilibrium

• Temperature

• Pressure

• Concentration

N2+ 2NH3+Heat3H2

Le ChatelierPrinciple

Sect: 7-5Word Wise

Math

Due: 1/15/09

Test: 1/16/09

Section 7-5

Worksheet

Due: 1/10/08

Test: 1/14/08