Ch. 9 NotesCh. 9 Notes88thth Grade Physical Science Grade Physical Science

By Lisa AnglimBy Lisa Anglim

9.1 Forming New 9.1 Forming New SubstancesSubstances

Chemical Chemical Reactions-Reactions-

The process by The process by which 1 or more which 1 or more substances undergo substances undergo change to produce 1 change to produce 1 or more different or more different substancessubstances

Reactions occur Reactions occur when chemical when chemical bonds are broken. bonds are broken. The atoms The atoms rearranged and form rearranged and form new bondsnew bonds

Clues that a reaction has Clues that a reaction has taken placetaken place

Formation of a gasFormation of a gas

Formation of a solidFormation of a solid

Color ChangeColor Change

Energy change – heat, cold, light or Energy change – heat, cold, light or sound producedsound produced

Conservation of Conservation of EnergyEnergy

Chemical reactions involve energyChemical reactions involve energyIt takes a certain amount of energy to start It takes a certain amount of energy to start the reaction (activation energy)the reaction (activation energy)Some reactions release more energy Some reactions release more energy (exothermic)(exothermic)Other reactions absorb energy Other reactions absorb energy (endothermic)(endothermic)

Energy is conserved just like mass. The Energy is conserved just like mass. The energy is always somewhere, in energy is always somewhere, in exothermic reactions it is stored in the exothermic reactions it is stored in the reactants and then released. In reactants and then released. In endothermic reactions it is stored in the endothermic reactions it is stored in the products.products.

Exothermic Exothermic Reactions:Reactions:

The energy of the reactants is greater The energy of the reactants is greater than the products. Energy is released than the products. Energy is released during the reaction in the form of light, during the reaction in the form of light, heat or electricity.heat or electricity.

Exothermic Exothermic ReactionReaction- Takes very little Takes very little

activation energy to activation energy to start the reactionstart the reaction

- Reactants have more Reactants have more energy stored in their energy stored in their bonds than the bonds than the productsproducts

- The extra energy will The extra energy will be released in the form be released in the form of heat and/or lightof heat and/or light

- ExamplesExamples

- Fire, glow stick, food Fire, glow stick, food

- Takes very little Takes very little activation energy to activation energy to start the reactionstart the reaction

- Reactants have more Reactants have more energy stored in their energy stored in their bonds than the bonds than the productsproducts

- The extra energy will The extra energy will be released in the form be released in the form of heat and/or lightof heat and/or light

- ExamplesExamples

- Fire, glow stick, food Fire, glow stick, food

Activation Energy

ReactantsEnergy given off

Products

Endothermic Endothermic Reactions:Reactions:

The energy of the reactants is less The energy of the reactants is less than the products. Energy is absorbed than the products. Energy is absorbed (the reaction requires energy to take (the reaction requires energy to take place)place)

Photosynthesis

Endothermic Endothermic ReactionReaction

Takes lots of activation Takes lots of activation energy to start the energy to start the reaction (hard to start)reaction (hard to start)

Products have more Products have more energy stored in their energy stored in their bonds than the bonds than the reactantsreactants

The extra energy is The extra energy is stored in the bonds of stored in the bonds of the molecules (like a the molecules (like a battery)battery)

ExamplesExamplesPhotosynthesis (energy Photosynthesis (energy absorbed from the sun), absorbed from the sun), photo paper, instant ice photo paper, instant ice packpack

Reactants

ProductsActivation Energy

Energy stored (absorbed)

9.2 9.2 Chemical Formula’s Chemical Formula’s and Equationsand Equations

Chemical FormulaChemical FormulaA shorthand A shorthand notation for a notation for a compound or a compound or a diatomic diatomic element using element using chemical chemical symbols and symbols and numbersnumbers

The formula gives you the names of the The formula gives you the names of the elements and tells you how many atoms elements and tells you how many atoms of each element are in that substance.of each element are in that substance.

The small numbers that are written The small numbers that are written below and to the right of the chemical below and to the right of the chemical symbols are called Subscripts, and symbols are called Subscripts, and notes the number of atoms of that notes the number of atoms of that element.element.

A number in front of a chemical formula A number in front of a chemical formula is a coefficient and it is multiplied by is a coefficient and it is multiplied by the subscript of all the atoms that are in the subscript of all the atoms that are in the formulathe formula

Chemical Formula’s

Chemical FormulaChemical Formula

the shorthand notation the shorthand notation for a compound using for a compound using chemical symbols and chemical symbols and numbersnumbers

SymbolsSymbols

Subscript goes with Subscript goes with the preceding symbolthe preceding symbol

CoefficientCoefficient

Diatomic moleculesDiatomic moleculesOO2 2

NN22

CompoundsCompoundsHH22OO

CC66HH1212OO66

Has 2 oxygen atoms

Has 2 nitrogen atoms

Has 2 hydrogen atoms and 1 oxygen

Has 6 carbon, 12 hydrogen and 6 oxygen atoms

CO25

Counting AtomsCounting Atoms

Mg (HCOMg (HCO33))2 2

means 1 Magnesium, 2 Hydrogen, 2 means 1 Magnesium, 2 Hydrogen, 2 Carbon atoms and 6 Oxygen atomsCarbon atoms and 6 Oxygen atoms

AgNOAgNO3 3

means 1 silver atom, 1 Nitrogen atom and means 1 silver atom, 1 Nitrogen atom and 3 oxygen atoms3 oxygen atoms

2 MgCl2 MgCl2 2 means 2 magnesium atoms and 4 chlorine means 2 magnesium atoms and 4 chlorine atomsatoms

Writing FormulasWriting Formulas

Ionic compoundsIonic compoundsRemember there Remember there must be a metal and must be a metal and a nonmetala nonmetal

Metal comes firstMetal comes first

Add “ide” to the Add “ide” to the end of the end of the nonmetalnonmetal

Ignore the Ignore the subscriptssubscripts

For exampleFor example

MgClMgCl22

Magnesium chlorineMagnesium chlorine

AlBrAlBr33

Aluminum bromideAluminum bromide

chloride

Examples of ionic compounds (the Examples of ionic compounds (the charges of the ions must be balanced)charges of the ions must be balanced)

Lithium fluorideLithium fluoride

Calcium oxideCalcium oxide

Lithium oxideLithium oxide

Calcium fluorideCalcium fluoride

Limetal nonmetal

Li+ FF-

LiFmetal nonmetal

CaCa+2 OO-2

CaO

metal nonmetal

Li+ O-2

LiOmetal nonmetal

Ca+2 F-

Charges are balanced

Charges are balanced

Charges are not balancedLi2OCharges are balanced

CaF Charges are not balanced

CaF2Charges are balanced

Covalent compoundsCovalent compoundsOnly nonmetals are Only nonmetals are foundfound

Use the prefixes to Use the prefixes to show the subscriptsshow the subscripts

““Mono” is not used Mono” is not used for the first for the first elements in the elements in the compoundcompound

Add “ide” to the last Add “ide” to the last nonmetal in the nonmetal in the formulaformula

For exampleFor example

COCO22Carbon dioxideCarbon dioxide

CHCH44Carbon tetrahydrideCarbon tetrahydride

HH22OODihydrogen Dihydrogen monoxidemonoxide

Prefixes

Mono- 1 Hexa- 6

Di- 2 Hepta- 7

Tri- 3 Octa- 8

Tetra- 4 Nona- 9

Penta- 5 Deca- 10

Caution: This is a lethal substance (kills thousands of people each year), can be used for rocket fuel, causes billions of dollars in damage, found everywhere

Chemical Chemical EquationsEquations

A shorthand description of a chemical A shorthand description of a chemical reactions using chemical symbols and reactions using chemical symbols and formulas.formulas.

C + OC + O22 COCO22

ReactantsProducts

(Yields)

Balancing Balancing EquationsEquations

Law of Law of Conservation of Conservation of MassMass

Matter is not created Matter is not created or destroyed in or destroyed in ordinary chemical ordinary chemical and physical changesand physical changes

This means that This means that chemical equations chemical equations must balance.must balance.

The number and The number and types of atoms that types of atoms that goes into a reaction goes into a reaction is the same as what is the same as what comes out.comes out.

ExampleExampleHydrogen and Hydrogen and oxygen mix to form oxygen mix to form water.water.

HH22 + O + O22 HH22OO

+

2 1 2

Equations can only be Equations can only be balanced by changing balanced by changing the coefficient, you the coefficient, you can notcan not change a change a subscript.subscript.

Balancing Chemical Balancing Chemical Equations PracticeEquations Practice

Follow along on your handout as we go through the Follow along on your handout as we go through the program.program.

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