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• The purpose of the equation is to

show what was present before the reaction (carbon and oxygen) and afterwards (carbon dioxide)

• The substances that undergo change are reactants (carbon and oxygen)

• New substances formed as a result of that change are called products

• REACTANTS PRODUCTS

• CARBON + OXYGEN CARBON DIOXIDE

• SIMPLIFY:C+O2 CO2

CHEMICAL EQUATION

• A CHEMICAL EQUATION IS A REPRESENTATION OF A CHEMICAL REACTION IN WHICH THE REACTANTS AND PRODUCTS ARE EXPRESSED AS FORMULAS.

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

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?

• 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?

ANSWER

• 2H2 + O2 2H2O

• WHICH MEANS:–TWO MOLECULES OF HYDROGEN

REACT WITH ONE MOLECULE OF OXYGEN TO YIELD TWO MOLECULES OF WATER

• http://PHSchool.com/webcodes10/index.cfm?wcprefix=ccp&wcsuffix=1071&area=view&x=13&y=7

MATH SKILLS

• READ OVER THE MATH SKILLS EXAMPLES AND STEPS FOR BALANCING EQUATIONS ON PAGE 195

• THEN, TRY THE MATH PRACTICE 1-3

Balancing equations tutorials

• http://www.youtube.com/watch?v=RnGu3xO2h74

• http://www.youtube.com/watch?v=gskm-dfKv5g

BELLWORK

• BALANCE THE FOLLOWING CHEMICAL EQUATION:

• H2+O2 H2O

• WHAT ARE SOME UNITS OF MEASURE THAT YOU KNOW OF?

A. What is the Mole?

• A counting number (like a dozen)

• Avogadro’s number (NA)

• 1 mol = 6.02 1023 items

A large amount!!!!

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

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!

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

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

LETS TRY

• MOLAR MASS OF C• MOLAR MASS OF Fe• MOLAR MASS OF H2O

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

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

BELLWORK

WHAT IS A MOLE?WHY DO WE USE MOLES?HOW MUCH IS ONE MOLE OF BARIUM IN GRAMS?CARBON DIOXIDE?WATER?

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

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

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

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/mole• Step 2: set up the equation

55 grams CO2 x 1 mol CO2 = ? mol CO2

44 grams CO2

• Step 3: Solve the equation55 grams CO2 x 1 mol CO2 = ? mol CO2 44 grams CO2

1/44= .022755 x .0227 = 1.25

There are 1.25 moles of CO2 in 55 grams of CO2

Flip it!

• Now, suppose we have 2.4 moles of sulfur.

• How do we find how many grams there are in 2.4 moles of sulfur?

• Step 1: Find the molar mass of sulfur.32.07 grams/mole

• Step 2: Set up the equation:2.4 moles x 32.07 grams S = ? Grams S

1 mol S

• Step 3: solve the equation:2.4 x 32.07 = 77 grams sulfer

There are 77 grams of sulfur in 2.4 moles of sulfur

Get into the groups I assigned the other day.

• Work on the worksheet together.• Do as many problems as you can.