chemical reactions
DESCRIPTION
Chemical Reactions. BELLWORK. BRIEFLY WRITE ABOUT A SCIENTIFIC OBSERVATION YOU MADE RECENTLY. Chemical equations. WE USE CHEMICAL EQUATIONS TO DESCRIBE CHEMICAL REACTIONS. Burning Coal. This is a chemical reaction - PowerPoint PPT PresentationTRANSCRIPT
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Chemical Reactions
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BELLWORK
• BRIEFLY WRITE ABOUT A SCIENTIFIC OBSERVATION YOU MADE RECENTLY
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Chemical equations
• WE USE CHEMICAL EQUATIONS TO DESCRIBE CHEMICAL REACTIONS
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Burning Coal
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• This is a chemical reaction• The purpose of the equation is to
show what was present before the reaction (carbon and oxygen) and afterwards (carbon dioxide)
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• The substances that undergo change are reactants (carbon and oxygen)
• New substances formed as a result of that change are called products
• REACTANTS PRODUCTS
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• CARBON + OXYGEN CARBON DIOXIDE
• SIMPLIFY:C+O2 CO2
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CHEMICAL EQUATION
• A CHEMICAL EQUATION IS A REPRESENTATION OF A CHEMICAL REACTION IN WHICH THE REACTANTS AND PRODUCTS ARE EXPRESSED AS FORMULAS.
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CONSERVATION OF MASS
• THE LAW OF THE CONSERVATION OF MASS: MASS IS NEITHER CREATED NOR DESTROYED IN A CHEMICAL REACTION
• ALTHOUGH THE MASS OF THE COAL WAS REDUCED DURING THE REACTION, IT WAS NOT LOST
• THE MASS OF THE CARBON DIOXIDE CREATED WAS EQUAL TO THE MASS OF THE COAL THAT WAS LOST
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BALANCING EQUATIONS
• ACCORDING TO THE LAW OF CONSERVATION OF MASS, EACH SIDE OF AN EQUATION MUST BE EQUAL
• H2 + O2 H2O
• WHAT IS WRONG WITH THIS EQUATION?
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• TO BALANCE WE SIMPLY ADD COEFFICIENTS:–THE NUMBERS THAT APPEAR BEFORE THE
EQUATIONH2 + O2 H2O =
H2 + O2 2H2O
• WHAT IS WRONG WITH THIS EQUATION?• HOW CAN WE FIX IT?
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ANSWER
• 2H2 + O2 2H2O
• WHICH MEANS:–TWO MOLECULES OF HYDROGEN
REACT WITH ONE MOLECULE OF OXYGEN TO YIELD TWO MOLECULES OF WATER
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• http://PHSchool.com/webcodes10/index.cfm?wcprefix=ccp&wcsuffix=1071&area=view&x=13&y=7
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MATH SKILLS
• READ OVER THE MATH SKILLS EXAMPLES AND STEPS FOR BALANCING EQUATIONS ON PAGE 195
• THEN, TRY THE MATH PRACTICE 1-3
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Balancing equations tutorials
• http://www.youtube.com/watch?v=RnGu3xO2h74
• http://www.youtube.com/watch?v=gskm-dfKv5g
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BELLWORK
• BALANCE THE FOLLOWING CHEMICAL EQUATION:
• H2+O2 H2O
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• WHAT ARE SOME UNITS OF MEASURE THAT YOU KNOW OF?
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A. What is the Mole?
• A counting number (like a dozen)
• Avogadro’s number (NA)
• 1 mol = 6.02 1023 items
A large amount!!!!
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Counting with Moles
• MOLE: (MOL) AN AMOUNT OF A SUBSTANCE THAT CONTAINS APPROXIMATELY 6.02 X 1023 PARTICLES OF THAT SUBSTANCE.
• KNOWN AS AVOGADRO’S NUMBER• A MOLE OF A SUBSTANCE GENERALLY
CONTAINS 6.02 X 1023 ATOMS, MOLECULES, OR IONS OF THAT SUBSTANCE
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1 mole of hockey pucks would equal the mass of the moon!
A. What is the Mole?
• 1 mole of pennies would cover the Earth 1/4 mile deep!
1 mole of basketballs would fill a bag the size of the earth!
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Molar Mass
• THE MASS OF DIFFERENT ELEMENTS ARE DIFFERENT, AS IS THEIR MOLAR MASS
• THE MOLAR MASS OF AN ELEMENT IN THE SAME AS ITS ATOMIC MASS EXPRESSED IN GRAMS
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MASS OF COMPOUNDS• YOU CAN FIND THE MASS OF
COMPOUNDS BY ADDING THE MASS OF THEIR COMPONENTS
• A CARBON DIOXIDE MOLECULE:• CARBON= 12 GRAMS• OXYGEN = 16 GRAMS X 2 = 32 GRAMS• 12 + 32 = 44 GRAMS• CARBON DIOXIDE HAS A MOLAR MASS
OF 44 GRAMS
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LETS TRY
• MOLAR MASS OF C• MOLAR MASS OF Fe• MOLAR MASS OF H2O
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MOLE-MASS CONVERSIONS
• TO FIND HOW MANY MOLES ARE IN A CERTAIN # OF GRAMS OF AN ELEMENT OR MOLECULE:
• Y GRAMS x1/z grams= x moles
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Example
• WE HAVE 55 GRAMS OF CO2
• HOW DO WE FIND HOW MANY MOLES WE HAVE?
• 55 X 1 mol/44 g• 1 mol/44 g=.02272727 mol• .02272727mol X 55 g = 1.25 mol CO2
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BELLWORK
WHAT IS A MOLE?WHY DO WE USE MOLES?HOW MUCH IS ONE MOLE OF BARIUM IN GRAMS?CARBON DIOXIDE?WATER?
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REVIEW:
• A mole is just a number, nothing else
• That number is 6.02 x 1023
• We use this number to make otherwise incredibly small numbers (such as the mass of an atom) easy to use in chemical formulas
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Review
• There are two conversions we will do with moles:–Find how many moles there are in a
certain number of grams (mass) an element or molecule
–Find the the number of grams (mass) there are in a certain number of moles of an element or molecule
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Two conversion factors
a) Grams b)1 Mol
1 Mol or Grams
How many grams, use conversion factor aHow many moles, use conversion factor b
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Practice
• Suppose we have 55 grams of CO2
• How do we find how many moles of CO2 there are in 55 grams of CO2?
• Step 1: find the molar mass of CO2
44 grams• Step 2: set up the equation
55 grams CO2 x 1 mol CO2 = ? mol CO2
44 grams CO2
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• Step 3: Solve the equation
55 grams CO2 x 1 mol CO2 = ? mol CO2
44 grams CO2
1/44=