PS 101

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PS 101

• Kim Cohn
• Email address
• Kcohn_at_academic.csubak.edu

2
5th Grade Standards 2

• Students know that images of atoms and molecules
  show there are often well ordered arrays.
• Students know differences in chemical and
  physical properties of substances can be used to
  separate mixtures.
• Students know properties of some substances such
  as sugar, salt, water, helium, oxygen, nitrogen
  and carbon dioxide.

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Chemical Equation 1

• Reactants ? Products
• C(s) O2(g) ? CO2(g)
• 1C(s) 1O2(g) ? 1CO2(g)
• 1 carbon atom reacts with 1 oxygen molecule to
  form 1 molecule of carbon dioxide.

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Chemical Equation 2

• Usually dont put in ones.
• C(s) O2(g) ? CO2(g)
• Conserve mass.
• The number of carbon atoms on the left is equal
  to the number of carbon atoms on the right.
• The same is true for oxygen atoms.

5
Balancing Equations

• Fe(s) O2(g) ? Fe2O3(s)
• Focus on one element at a time.
• One Fe on left, two on right.
• Put a two in front of the Fe on the left.
• 2Fe(s) O2(g) ? Fe2O3(s)
• Now try oxygen

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Balancing Equations 2

• 2Fe(s) O2(g) ? Fe2O3(s)
• Now try oxygen.
• There are 2 on the left and three on the right.
• You can not change subscripts.
• 2Fe(s) 3O2(g) ? 2Fe2O3(s)
• Fe is now wrong.
• 4Fe(s) 3O2(g) ? 2Fe2O3(s)

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Balancing Equations 3

• Try to balance
  H2(g) N2(g) ? NH3(g)
• 3H2(g) N2(g) ? 2NH3(g)
• Try to balance
  CH4(g) O2(g) ? CO2(g) H2O(l)

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Balancing Equations 4

• Remember - conserve mass.
• There are 12 yellow atoms on right, therefore
  there must be atoms on the left.
• The yellow atoms on the right are found in the
  molecule yellow2.
• The yellow atoms on the left are found in the
  solid (red yellow).

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Energy

• If the products have less potential energy than
  the reactants, the reaction will give off energy
  during the reaction.
• This type of reaction is called exothermic.
• The energy is usually given off in the form of
  heat.
• Lighting a match, burning food.

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Energy 2

• Sometimes you need to put energy in to have a
  reaction occur.
• This type of reaction is called endothermic.
• For example, melting ice,
• charging a battery.

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Catalyst

• A compound that speeds up a reaction without
  being changed is called a catalyst.
• Enzymes in your mouth change starch into sugar.
• Gasoline is burned more quickly in the presence
  of platinum.
• Your catalytic converter uses platinum to burn
  all of the gasoline.

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Cultural Enrichment

• Next time you are sitting at a bar bet the
  person next to you they cant make a sugar cube
  burn, but you can.
• If you try to light a sugar cube on fire it goes
  out.
• If you rub the cube in the ashes of cigarette it
  will burn.
• There are enough metal ions in the ash to act as
  a catalyst for the reaction.

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Ozone 1

• Oxygen atoms are usually found as the oxygen
  molecule, O2.
• It is possible for three oxygen atoms to bind
  together to form the more energetic ozone
  molecule, O3.
• At sea level ozone is bad for you.
• It destroys rubber, causes smog.

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Ozone 2

• In the upper atmosphere, ozone is good for you.
• It absorbs harmful ultraviolet radiation.
• Too much ultraviolet radiation causes skin and
  plant damage.
• Molecules that contain the fluorine atom destroy
  ozone.

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Ozone 3

• On the left of the screen is a typical molecule,
  difluorodichloromethane, found in cooling
  systems.
• C-Cl and C-F bonds are very stable and long
  lasting.
• The compound is volatile and floats to the upper
  atmosphere where it will destroy the ozone.
• Such compounds are no longer being used.

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Ozone 4

• We are not sure destruction of the ozone in the
  atmosphere occurs to any appreciable extent and
• Substitutes for CF2Cl2 (refrigerants) are not as
  good and
• The substitutes are more expensive.
• The question revolves around risk/reward ratios.
• Discussion.

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Chemical Equilibrium

• The object of the game is to get as many balls in
  your opponents court as possible.

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Chemical Equilibrium 2

• At the start of the game B is winning.

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Chemical Equilibrium 3

• After a few minutes A has enough balls to start
  throwing them back.

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Chemical Equilibrium 4

• After a few more minutes there are just as many
  balls in As court as B.

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Chemical Equilibrium 5

• Now both A and B are throwing balls back and
  forth without any change in the number of balls
  on each side.

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Chemical Equilibrium 6

• This is an equilibrium condition.

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Chemical Equilibrium 7

• If B were bigger and stronger, the equilibrium
  would lie to the left.

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Chemical Equilibrium 8

• The same sort of equilibrium occurs with chemical
  reactions.
• The equilibrium can be affected by temperature
  and pressure.
• You are most familiar with the physical
  equilibrium between ice and water.

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Chemical Equilibrium 9

• When water turns to ice it gives off heat.
• Water ? Ice heat.
• If you add heat to ice, the reaction goes to the
  ?

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Chemical Equilibrium 10

• If the reaction gives off heat, the addition of
  heat pushes the reaction to the ?
• Consider opening a can of soda pop.
• Soda pop ? water gas.
• This reaction makes more gas molecules on the
  right of the reaction than on the left, the
  addition of pressure causes the reaction to go to
  the ?

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Chemical Equilibrium 11

• When you burn gasoline in your car you also burn
  or oxidize some nitrogen to form NO2.
• NO2 will dimerize
• 2NO2 ? N2O4 Energy.
• NO2 is dark brown, N2O4 is light brown.
• Why is the air brown over LA in the summer?

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Relative Masses 1

• A recipe calls for an equal number of both
  grapefruits and lemons.
• You could count both items in the store or
• Weigh them.
• You would not buy equal weights of both because
  grapefruits weigh more than lemons.

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Relative Masses 2

• Consider
  1C(s) 1O2(g) ? 1CO2(g)
• This recipe calls for 1 carbon atom and 1 oxygen
  molecule to make 1 molecule of CO2 , carbon
  dioxide.

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Relative Masses 3

• 1C(s) 1O2(g) ? 1CO2(g)
• If you wanted to make CO2 you could count out 1
  carbon atom and 1 oxygen molecule and put them
  together to make a molecule of CO2.
• Because atoms and molecules are too small to see
  you cant count them out.

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Relative Masses 3

• Because you cant count atoms and molecules to
  use the recipe and make CO2 we need to weigh
  atoms or molecules.
• To get the right proportions, we need to know the
  relative masses.
• We do!
• The atomic masses the relative masses.

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Relative Masses 4

• On the periodic table the atomic mass is usually
  placed under the symbol for the atom.

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Relative Masses 6

• C(s) O2(g) ? CO2(g)
• The atomic mass of C is 12.00.
• The atomic mass of one oxygen atom is 16.00.
• The oxygen molecule contains two oxygen atoms and
  has a relative mass of (2 x 16) or 32.
• Therefore 12.00 g of carbon will react with 32.00
  g of O2.

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Relative Masses 7

• 12.00 g of carbon will react with 32.00 g of O2.
• Or 12.00 oz. of carbon will react with 32.00 oz.
  of O2.
• Or 12.00 pounds of carbon will react with ?
• 32.00 pounds of O2.

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Relative Masses 8

• C(s) O2(g) ? CO2(g)
• The atomic mass of C is 12.00, and of O2 is 32.
• 12.00 g of carbon will react with 32.00 g of O2.
• g of carbon will react with 8.00 g of O2?
• 3.00 g of C
• Here is the way you solved the problem.

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Relative Masses 9

• First you realized that 12 g of C react with 32 g
  of O2
• To determine how many g of C react with 8.00 g of
  O2 you set up the proportion -

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Relative Masses 10

• And then you solved for X

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Relative Masses 11

• C(s) O2(g) ? CO2(g)
• The atomic mass of C is 12.00, and of O2 is 32.
• 12.00 g of carbon will react with 32.00 g of O2.
• g of O2 will react with 6.00 g of C?
• 16 g of O2

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Relative Masses 12

• C(s) O2(g) ? CO2(g)
• 32 g of O2 will react with 1000 g of C to produce
  g of CO2?
• In this case there is more than enough C so that
  the only limitation on the amount of carbon
  dioxide produced is on the amount of oxygen.
• Out of the 1000 g of C you will only use up 12 g
  of C.
• 44.00 g of CO2 will be produced.

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Relative Masses 13A

• C(s) O2(g) ? CO2(g)
• The atomic mass of C is 12.00, O2 is 32.
• 12.00 g of carbon will react with 32.00 g of O2.
• Here is a harder problem
• 12 g of O2 will react with 8.00 g of C to produce
  g of CO2?

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Relative Masses 13B

• 12 g of O2 will react with 8.00 g of C to produce
  g of CO2?
• If you had enough C, 12 g of O2 would make 12/32
  the amount of CO2 or
• (12/32) x 44 16.5 g of CO2
• If you had enough O2,8 g of C would make 8/12 the
  amount of CO2 or 29.3 g of CO2

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Relative Masses 14

• C(s) O2(g) ? CO2(g)
• Remember that 6.02 x 1023 of anything is a
• Mole.
• Therefore, you can say that one mole of carbon
  reacts with one mole of oxygen molecules to form
  one mole of carbon dioxide.

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Relative Masses 15

• Most chemists will say the atomic mass of a
  substance is equal to its weight in grams and
• The molecular mass of a substance is equal to
  its weight in grams.
• Consequently 12 g of C contains 6.02 x 1023 atoms
  of C.
• Each atom weighs 12/6.02 x 1023 g or
• 2 x 10-23 g

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Relative Masses 16

• What is the weight of 1 atom of C?
• 6.02 x 1023 atoms weigh 12.01 g
• Therefore 1 atom weighs
• 12.01 divided by 6.02 x 1023 or about
• 2.0 x 10-23 g