Physical SciencePhysical Science

Ch. 24Ch. 24

Section 1Section 1

Chemical ChangesChemical Changes

• Chemical ReactionChemical Reaction–Change in which one or Change in which one or more substances are more substances are converted into new converted into new substancessubstances

• ReactantReactant–Substances that reactSubstances that react

• ProductsProducts–New substances producedNew substances produced

Chemical ReactionChemical ReactionLeft sideLeft side right sideright side

produceproduce

reactants reactants products products

yieldsyields

Lavoisier’s ContributionLavoisier’s Contribution• Scientist who carried out Scientist who carried out

thousands of experiments to thousands of experiments to establish what we know as the establish what we know as the Conservation of MassConservation of Mass

• Conservation of MassConservation of Mass–Matter can neither be created nor Matter can neither be created nor

destroyed it just changes formsdestroyed it just changes forms

Produces, yields, formsProduces, yields, forms

++ PlusPlus

(s)(s) SolidSolid

(l)(l) LiquidLiquid

(g)(g) GasGas

(aq)(aq) Aqueous, substance Aqueous, substance dissolved in waterdissolved in water

heatheat

The reactants are heatedThe reactants are heated

lightlight

The reactants are The reactants are exposed to lightexposed to light

elec.elec.

An electric current is An electric current is applied to the reactantapplied to the reactant

• Chemical EquationChemical Equation–A way to describe a chemical A way to describe a chemical

reaction using chemical reaction using chemical formulas and other symbolsformulas and other symbols

• CoefficientsCoefficients–Tells the number of units of Tells the number of units of

each substance taking place each substance taking place in a reactionin a reaction

–Only way to Only way to BALANCEBALANCE a a chemical equationchemical equation

Section 2Section 2

Chemical EquationsChemical Equations

Balancing Chemical EquationsBalancing Chemical Equations–Does not change the Does not change the

substances involved or what substances involved or what happens within a reaction, it happens within a reaction, it only changes the way the only changes the way the reaction is reaction is REPRESENTEDREPRESENTED..

• Balanced Chemical EquationBalanced Chemical Equation–Same number of atoms on Same number of atoms on

both sides of the equationboth sides of the equation

How to Balance EquationsHow to Balance Equations1.1. Write chemical equation using Write chemical equation using symbols & formulassymbols & formulas

2.2. List elements involvedList elements involved

3.3. List number of atoms for each List number of atoms for each element involved on each sideelement involved on each side

4.4.Choose coefficients to balance the Choose coefficients to balance the equationequation

5.5. Recheck number of atoms for Recheck number of atoms for each element involved on each sideeach element involved on each side

Things to rememberThings to rememberwhen balancing equationswhen balancing equations

• Diatomic MoleculesDiatomic Molecules–Br, O, F, I, N, Cl, HBr, O, F, I, N, Cl, H

• Save Oxygen and Hydrogen Save Oxygen and Hydrogen to last to balanceto last to balance–Most times they balance Most times they balance

themselves as other elements themselves as other elements are balancedare balanced

1.1. Al + BrAl + Br22 AlBr AlBr33

2.2. Bi + OBi + O22 Bi Bi22OO55

3.3. Al + C Al + C Al Al44CC33

4.4. AgS + Ni AgS + Ni NiS NiS22 + Ag + Ag

5.5. PbO +PbO + NaCl NaCl PbCl PbCl22 + Na + Na22OO

Al + BrAl + Br22 AlBr AlBr33

AlAl BrBr

11 22

11 22

22

AlAl BrBr

11 33

11 33

2Al + 3Br2Al + 3Br22 2AlBr 2AlBr33

Bi + OBi + O22 Bi Bi22OO55

BiBi OO

11 22

11 22

11 22

11 22

22

BiBi OO

22 55

22 55

4Bi + 5O4Bi + 5O22 2Bi 2Bi22OO55

Al + C Al + C Al Al44CC33

AlAl CC

11 11

11 11

11 11

11

AlAl CC

44 33

4Al + 3C 4Al + 3C Al Al44CC33

AgS + Ni AgS + Ni NiS NiS22 + Ag + Ag

AgAg SS NiNi

11 11 11

11 11

AgAg SS NiNi

11 22 11

11

2AgS + Ni 2AgS + Ni NiS NiS22 + 2Ag + 2Ag

PbO +PbO + NaCl NaCl PbCl PbCl22 + Na + Na22OO

PbPb OO NaNa ClCl

11 11 11 11

11 11

PbPb OO NaNa ClCl

11 11 22 22

PbO +PbO + 2NaCl 2NaCl PbCl PbCl22 + Na + Na22OO

Section 3Section 3

ClassifyingClassifyingChemical ReactionsChemical Reactions

Types of ReactionsTypes of Reactions

1.1. SynthesisSynthesis

2.2. DecompositionDecomposition

3.3. Single DisplacementSingle Displacement

4.4. Double DisplacementDouble Displacement

SynthesisSynthesis• Two or more substances Two or more substances

reacting (combine) to form a reacting (combine) to form a new substancenew substance

A + B A + B AB AB

2H2H22 + O + O22 2H 2H22OO

DecompositionDecomposition• One substance reacting One substance reacting

(decomposes or breaks down) (decomposes or breaks down) to form two or more new to form two or more new substancessubstances

AB AB A + B A + B

2H2H22O O 2H 2H22 + O + O22

Single DisplacementSingle Displacement• When one element replaces When one element replaces

another element within a another element within a compoundcompound

AB + C AB + C AC + B AC + BAB + C AB + C CB + A CB + A

Cu + 2AgS Cu + 2AgS CuS CuS2 2 + 2Ag+ 2Ag

Double DisplacementDouble Displacement• Positive ion of one compound Positive ion of one compound

replaces the positive ion of the replaces the positive ion of the other to form two new other to form two new compoundscompounds

AB + CD AB + CD AD + CB AD + CB

HH22O + AgS O + AgS H H22S + AgOS + AgO

• PrecipitatePrecipitate–An insoluble compound An insoluble compound

that comes out of solution that comes out of solution during a during a double double displacement reactiondisplacement reaction

Section 4Section 4

Chemical ReactionsChemical Reactionsand Energyand Energy

More Energy OutMore Energy Out• Exergonic ReactionsExergonic Reactions

–Chemical reactions that Chemical reactions that release energyrelease energy

• Exothermic ReactionsExothermic Reactions–When the energy given off When the energy given off

in a reaction is primarily in in a reaction is primarily in the form of heatthe form of heat

More Energy InMore Energy In• Endergonic ReactionsEndergonic Reactions

– When a chemical reactions requires more When a chemical reactions requires more energy to break bonds than is released energy to break bonds than is released when new ones are formedwhen new ones are formed

– Energy absorbed can be in the form of Energy absorbed can be in the form of light, heat, or electricitylight, heat, or electricity

• Endothermic ReactionsEndothermic Reactions– When energy needed is in the form of heatWhen energy needed is in the form of heat

• Endothermic refers not just to reactionsEndothermic refers not just to reactions–Also refers to physical changesAlso refers to physical changes–Epsom salt dissolving in waterEpsom salt dissolving in water– Ice pack / Cold PackIce pack / Cold Pack

• CatalystsCatalysts–A substance that speeds up a A substance that speeds up a

chemical reaction without chemical reaction without being permanently changed being permanently changed itselfitself

• When you add a catalysts the When you add a catalysts the mass of the product formed mass of the product formed remains the same, but it will remains the same, but it will form more rapidlyform more rapidly

• InhibitorsInhibitors–Substances that are used to Substances that are used to

combine with one of the combine with one of the reactants to prevent certain reactants to prevent certain reactions from occuringreactions from occuring

–Ex. Food preservativesEx. Food preservatives• They prevent chemical They prevent chemical reactions that would cause the reactions that would cause the food to spoilfood to spoil