Upload
posy-holmes
View
220
Download
0
Tags:
Embed Size (px)
Citation preview
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.
IN OUT
More Review