Chemical ReactionsChemical ReactionsSection 1: Observing Chemical ChangesSection 1: Observing Chemical Changes

How can changes in matter be described?How can changes in matter be described?

In terms of two kinds In terms of two kinds of properties- of properties- physicalphysical properties properties and and chemicalchemical propertiesproperties

Changes in matter Changes in matter can be described in can be described in terms of physical or terms of physical or chemical chemical changeschanges

What is a physical property?What is a physical property?

A characteristic of A characteristic of a substance that a substance that can be observed can be observed withoutwithout changing changing the substance into the substance into another substanceanother substance

Examples: ice Examples: ice melting, melting, colorcolor, , hardness, texture, hardness, texture, shine, etc.shine, etc.

What is a chemical property?What is a chemical property? A characteristic of a A characteristic of a

substance that describes substance that describes its ability to its ability to changechange into into other other substancessubstances

Examples: burning Examples: burning magnesium, magnesium, rustingrusting

Substances that undergo chemical changes – reactants

The new substance formed - product

What is the difference between a What is the difference between a physical and a chemical physical and a chemical

reaction?reaction? A change in matter A change in matter

that produces one that produces one or more or more newnew substances is a substances is a chemical chemical changechange, or , or chemical chemical reactionreaction

Physical change Physical change examples: braiding examples: braiding your hair, squashing your hair, squashing a a marshmallowmarshmallow

Chemical change Chemical change examples: examples: burningburning of gasoline, burning of gasoline, burning a marshmallowa marshmallow

How can you tell when a How can you tell when a chemical reaction occurs?chemical reaction occurs?

Chemical changes Chemical changes occur when bonds occur when bonds breakbreak and new and new bonds bonds formform

Chemical reactions Chemical reactions involve two main involve two main kinds of changes kinds of changes that you can that you can observe-formation observe-formation of new of new substancessubstances and changes in and changes in energyenergy

What are some changes in What are some changes in properties that indicate a properties that indicate a

chemical change?chemical change? Precipitate – a Precipitate – a

solidsolid that forms that forms from a solution from a solution during a chemical during a chemical reactionreaction

ColorColor change may change may indicate a indicate a chemical reactionchemical reaction

Gas production – Gas production – bubblesbubbles

How do you categorize changes How do you categorize changes in energy?in energy?

Endothermic – A Endothermic – A reaction in which reaction in which energy is energy is absorbedabsorbed– More energy is More energy is

required to break the required to break the bond of the bond of the reactants than is reactants than is released by the released by the formation of the new formation of the new productsproducts

– Examples: baking Examples: baking soda and vinegar soda and vinegar gets cooler when gets cooler when combinedcombined

Exothermic – A Exothermic – A reaction that reaction that releasesreleases energy in energy in the form of the form of heatheat– The energy released The energy released

as the products form as the products form is greater than the is greater than the energy required to energy required to break the bonds of break the bonds of the reactantsthe reactants

– Examples: burning Examples: burning of airplane fuelof airplane fuel

endothermicendothermic exothermicexothermic

Section 2: Describing chemical reactionsSection 2: Describing chemical reactionsWhat information does a chemical equation What information does a chemical equation

contain?contain? Chemical equations Chemical equations

use chemical use chemical formulasformulas and other and other symbols instead of symbols instead of words to summarize words to summarize a reactiona reaction

Reactants – Reactants – substances you have substances you have at the at the beginningbeginning

Products – new Products – new substances substances produced when the produced when the reaction is reaction is completecomplete

What does the principle of What does the principle of conservation of mass state?conservation of mass state?

That in a That in a chemical chemical reaction, the total reaction, the total massmass of the of the reactantsreactants must must equal the total equal the total mass of the mass of the productsproducts

Matter is neither Matter is neither created nor created nor destroyeddestroyed

What does open or closed What does open or closed system mean?system mean?

Open system – Open system – matter can matter can enterenter from or escape from or escape to the to the surroundingssurroundings

Closed system – Closed system – matter is not matter is not allowed to enter allowed to enter or or leaveleave

What must a balanced chemical What must a balanced chemical equation show?equation show?

The same The same numbernumber of of each type of each type of atomatom on on both sides of the both sides of the equationequation

Represents the Represents the conservation of conservation of massmass

Coefficients – a Coefficients – a number placed in number placed in frontfront of a chemical formula of a chemical formula in an equation that in an equation that tells you how many tells you how many atomsatoms or molecules of or molecules of a reactant or product a reactant or product take place in the take place in the reactionreaction

How do you balance chemical equations?How do you balance chemical equations?

Count the # of Count the # of atomsatoms of of each element in the each element in the reactants & productsreactants & products

ID element that is ID element that is notnot equal equal on both sideson both sides

Add Add coefficientcoefficient to the front to the front of the formula that will of the formula that will make the # = on both sides make the # = on both sides for that elementfor that element

Sample ProblemsSample ProblemsSample Problem:Sample Problem:Zn + HBr Zn + HBr H H22 + ZnBr + ZnBr22

Multiply HBr x 2 to correct Multiply HBr x 2 to correct (balance)(balance)

Zn + 2HBr Zn + 2HBr H H22 + ZnBr + ZnBr22

ReactantsReactants ProductsProducts

1 Zn1 Zn 1 Zn1 Zn

1 H1 H 2 H2 H

1 Br1 Br 2 Br2 Br

ReactantsReactants ProductsProducts

1 Zn1 Zn 1 Zn1 Zn

2 H2 H 2 H2 H

2 Br2 Br 2 Br2 Br

Try these!!Try these!! Na + ClNa + Cl22 NaCl NaCl

Ca + ClCa + Cl22 CaCl CaCl22

HH22O O H H22 + O + O22

NN22 + H + H22 NH NH33

AlAl22OO33 Al + O Al + O22

PP44 + O + O22 P P44OO66

Fe + HFe + H22O O Fe Fe33OO44 + H + H22

2

2

2

3

3

2

2

4

3

3

2

4

4

What are the three categories of What are the three categories of chemical reactions?chemical reactions?

SynthesisSynthesis DecompositionDecomposition ReplacementReplacement

What is a synthesis reaction?What is a synthesis reaction? When When twotwo or more or more

substances combine to substances combine to make a more complex make a more complex substancesubstance

–A + B A + B AB AB

–2H2H22 + O + O22 2H2H22OO Example: hydrogen and Example: hydrogen and

oxygen to make oxygen to make waterwater

What is a Decomposition What is a Decomposition reaction?reaction?

BreakingBreaking down compounds into down compounds into simpler productssimpler products

–AB AB A + B A + B

–2H2H22OO22 2H 2H22O + OO + O22 Example: Example: HydrogenHydrogen peroxide peroxide

decomposes into water and decomposes into water and oxygen gasoxygen gas

What is a replacement What is a replacement reaction?reaction?

When one element When one element replacesreplaces another in a another in a compound, or when two elements in compound, or when two elements in different compounds different compounds tradetrade places places

Example: copper metal obtained by Example: copper metal obtained by heating copper oxide with carbonheating copper oxide with carbon

Single (one element replaces Single (one element replaces anotheranother) )

– AB + C AB + C AC + B AC + B– Zn + 2HCl Zn + 2HCl ZnCl ZnCl22 + H + H22

or double (elements appear to trade places or double (elements appear to trade places with another with another compoundcompound))

– AB + CD AB + CD AC + BD AC + BD– NaCl + AgF NaCl + AgF NaF +AgCl NaF +AgCl

Section 3: Controlling Chemical ReactionsSection 3: Controlling Chemical ReactionsHow is activation energy related to chemical How is activation energy related to chemical

reactions?reactions? The minimum The minimum

amountamount of energy of energy needed to start a needed to start a chemical reactionchemical reaction

All chemical All chemical reactions need a reactions need a certain amount of certain amount of activation activation energyenergy to get startedto get started

What factors affect the rate of a What factors affect the rate of a chemical reaction?chemical reaction?

SurfaceSurface area – the greater the surface area that area – the greater the surface area that faster the reaction (ex. Chewing)faster the reaction (ex. Chewing)

TemperatureTemperature – raising the temperature causes – raising the temperature causes particles to move faster and therefore have more particles to move faster and therefore have more energy; they also come into contact more often; energy; they also come into contact more often; lowering temperature slows things down lowering temperature slows things down

Concentration – amount of substance in a given Concentration – amount of substance in a given volumevolume; increased concentration-increased ; increased concentration-increased reactionreaction

Catalysts – increases the rate of a Catalysts – increases the rate of a reactionreaction by by decreasing the energy needed to startdecreasing the energy needed to start– Enzymes: biological catalystsEnzymes: biological catalysts

Inhibitors – material used to Inhibitors – material used to decreasedecrease the rate of the rate of reaction (ex. preservatives in food)reaction (ex. preservatives in food)