Chemical vs. Chemical vs. Physical ChangesPhysical Changes

the substances are not altered chemically, but are merely changed to another phase (i.e. gas, liquid, solid) or separated or combined.

•No change occurs in the identity of the substance

Physical Change

Chemical change

the substances are altered chemically and display different physical and chemical properties after the change.

Atoms in the reactants are rearranged to form one or more different substances

Old bonds are broken; new bonds form

Indicators/Signs of a Indicators/Signs of a Chemical ChangeChemical Change(these are not fool proof)(these are not fool proof)

CChemists hemists GGet et PPractice ractice TTrying rying LLabsabs– Color changeColor change– Gas/bubblesGas/bubbles– Precipitate, ppt (a solid forms)Precipitate, ppt (a solid forms)– Temperature changeTemperature change

Exothermic (hot) or endothermic (cold)Exothermic (hot) or endothermic (cold)

– Light given offLight given offTypically, more than one indicator will be

seen.

Learning CheckLearning Check

Classify each of the following as aClassify each of the following as a

1) physical change or 2) chemical change1) physical change or 2) chemical change

A. ____ a burning candleA. ____ a burning candle

B. ____ melting iceB. ____ melting ice

C. ____ toasting a marshmallowC. ____ toasting a marshmallow

D. ____ cutting a pizzaD. ____ cutting a pizza

E. ____ Tarnished silverE. ____ Tarnished silver

SolutionSolution

Classify each of the following as aClassify each of the following as a

1) physical change or 2) chemical change1) physical change or 2) chemical change

A. __A. __22__ a burning candle__ a burning candle

B. __B. __11_ melting ice_ melting ice

C. __C. __22__ toasting a marshmallow__ toasting a marshmallow

D. __D. __11__ cutting a pizza__ cutting a pizza

E. __E. __22__ tarnished silver __ tarnished silver

Chemical ReactionChemical Reaction

A process in which at least A process in which at least one new substance is one new substance is produced as a result of produced as a result of chemical change.chemical change.

In a chemical reactionIn a chemical reaction The way atoms are joined is changedThe way atoms are joined is changed Atoms aren’t created or destroyed.Atoms aren’t created or destroyed. Can be described several ways:Can be described several ways:

– In a sentence In a sentence Copper reacts with chlorine to form copper Copper reacts with chlorine to form copper

(II) chloride.(II) chloride.

– In a In a word equationword equation Copper + chlorine Copper + chlorine copper (II) chloride copper (II) chloride

– FormulasFormulas Cu+ ClCu+ Cl22 CuCl CuCl22

A Chemical EquationA Chemical Equation

Reactants Reactants ProductsProducts

Conservation of Mass and EnergyConservation of Mass and Energy

Mass and Energy cannot Mass and Energy cannot be created or destroyed, be created or destroyed, but can change formbut can change form

Symbols used in Symbols used in equationsequations separates the reactants from productsseparates the reactants from products

– Read as “reacts to form” or “yields”Read as “reacts to form” or “yields” + read as “and” or “reacts with”+ read as “and” or “reacts with” (s) after the formula -solid(s) after the formula -solid (g) after the formula -gas(g) after the formula -gas (l) after the formula –liquid(l) after the formula –liquid (aq) after the formula- aqueous solution(aq) after the formula- aqueous solution

– Dissolved in water.Dissolved in water.

More Symbols used in More Symbols used in EquationsEquations

used after a product indicates a used after a product indicates a gas; gas; same as (g)same as (g)

used after a product indicates a used after a product indicates a solid or ppt (precipitate); same as solid or ppt (precipitate); same as (s)(s)

Even More Symbols used Even More Symbols used in Equationsin Equations

indicates a reversible indicates a reversible reaction (More later)reaction (More later)

shows that shows that heat is supplied to the reactionheat is supplied to the reaction

is used to indicate a catalyst is used to indicate a catalyst used supplied, in this case, platinum.used supplied, in this case, platinum.

heat ,

Pt

What is a catalyst?What is a catalyst?

A substance that speeds up a A substance that speeds up a reaction without being changed reaction without being changed by the reaction.by the reaction.

Enzymes are biological or protein Enzymes are biological or protein catalysts.catalysts.

Diatomic elementsDiatomic elements

There are 8 elements that never want There are 8 elements that never want to be alone.to be alone.

If they are not with another element, If they are not with another element, they form diatomic molecules.they form diatomic molecules.

HH22 , N , N22 , O , O22 , F , F22 , Cl , Cl22 , Br , Br22 , I , I22 , and At , and At22 Brother HON CLIFBrother HON CLIF 1 + 7 pattern on the periodic table1 + 7 pattern on the periodic table

Sulfur & PhosphorusSulfur & PhosphorusSulfur, when alone, exists as SSulfur, when alone, exists as S88

Phosphorus, when alone, exists as Phosphorus, when alone, exists as PP44