Chemical Equations

1

• Chemical Equations
• Unit 3 Module 1

2
Counting Atoms Review

• Co-efficient
• The large number in front of a compound
  representing the number of units taking part in
  the reaction
• Subscript
• Tells how many atoms are in each molecule
• Subscripts counted for that element only
• H2O 2 ATOMS of HYDROGEN

3
Counting Atoms Review

• Coefficients counted for every element in the
  compound
• 2 H2O
• H 4
• O 2
• 4Al2(SO4)3
• Aluminum 2 4 8
• Sulfur 13 3 4 12
• Oxygen 4 3 12 4 48

4
Chemical Reactions

• When bonds are broken and new bonds are formed
• Energy is released from the old bonds and stored
  in the new bonds
• New combination of elements
• Chemical properties in new substances are
  different from the properties of the old
  substances

5
Evidence of Chemical Reactions

• A gas is formed (Bubbles)
• A Precipitate is formed (Turns cloudy because a
  new solid forms)
• There is a energy / temperature change (Because
  bonds are breaking and re-forming)
• There is a color change (Because new substances
  are forming
• Light is produced

6
Chemical Equations

• An expression that describes a chemical reaction
• 2Mg O2 2MgO

7
Chemical Equation Language

• REACTANTS PRODUCTS
• 2Mg O2 2MgO
• Reactants
• On the left of the arrow
• The elements/compounds you start with
• 2Mg O2
• Products
• On the right of the arrow
• The elements/ compounds you finish with
• 2MgO

8
Chemical Equation Language

• REACTANTS PRODUCTS
• Arrow
• Yields or Results in
• Separates the reactants from the products

9
Chemical Equation Language

• 3Fe(s) 4H2O(l) 1Fe3O4(aq) 4H2(g)
• (s)
• This Reactant is in SOLID form
• (l)
• This Reactant is in LIQUID form
• (aq)
• This Product is in AQUEOUS form (Mixed with
  Water)
• (g)
• This Product is in GAS form

10
Practice Counting Atoms

• Fe(SO4)
• Fe
• S
• O
• 4Cu(SO4)
• Cu
• S
• O
• 6Zn(NO3)2
• Zn
• N
• O

11
Practice Equations

• ZnBr2 2Ag(NO3) Zn(NO3)2 2AgBr
• What are the reactants?
• What are the products?
• How many molecules are there of AgBr?
• How many atoms of Oxygen are there in Ag(NO3)?

12
Law of Conservation of Mass

• Mass (matter) can be neither created or destroyed
  
• It just changes from one form to another
• Example BURNED WOOD
• 500g Wood 300g Ash 200g Smoke
• Reactant 500g Wood
• Product 300g Ash 200g Smoke
• TOTAL MASS OF THE PRODUCTS OF A REACTION IS EQUAL
  TO THE TOTAL MASS OF THE REACTANTS.

13
Law of Conservation of Mass

• 2KClO3 2KCl 3O2
• If 500 grams of KClO3 decomposes (breakdowns) and
  produces 303 grams of KCl, how many grams of O2
  are produced?
• 500 grams 303 grams ?
• 500 grams 303 grams 197 grams

14
Law of Conservation of Mass

• 2KI Pb(NO3)2 PbI2 K(NO3)
• If 700 grams of the product is produced, how many
  grams of KI do you start with if you also have
  520 grams of Pb(NO3)2?
• 520 grams ? 700 grams
• 520 grams 180 grams 700 grams

15
Law of Conservation of Mass

• 2H2S O2 H2O S
• If you have 250 grams of water and 380 grams of
  sulfur, how many grams of oxygen do you have if
  you start with 400 grams of H2S?
• ? 400g 250g 380g
• ? 400g 630g
• 230g 400g 630g

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Balanced Chemical Equations

• Shows Chemical Reactions in a Conservation of
  Mass form
• The total mass of the reactants MUST equal the
  total mass of the products
• A BALANCED EQUATION has the same ELEMENTS the
  same OF ATOMS in BOTH the reactants and
  products

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Balancing Chemical Equations

• IN A CHEMICAL EQUATION, THE TYPE OF ATOMS ON
  BOTH SIDES MUST BE EQUAL!!
• THIS IS NOT BALANCED!!!!
• H2 O2 H2O
• H 2 H 2
• O 2 O 1

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Balancing Chemical Equations

• ONLY CO-EFFICIENTS MAY BE CHANGED OR ADDED TO
  BALANCE AN EQUATION!!!
• THE NUMBER BEFORE THE COMPOUND
• SUBSCRIPTS MAY NOT BE CHANGED OR ADDED!!!!!
• THE SMALL NUMBER AFTER THE COMPOUND
• 2H2 O2 2H2O
• BALANCED

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How to Balance

• Write the equation with boxes in front of each
  compound
• H2 O2 H2O
• Count the of atoms of each element in the
  reactants and the products
• H 2 H 2
• O 2 O 1
• If any numbers are different, the equation is NOT
  balanced

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How to Balance

• Change ONLY the coefficients to balance the
  equation
• H2 O2 2 H2O
• H 2 H 2 4
• O 2 O 1 2
• The equation is BALANCED when the same number of
  atoms of each element are on BOTH sides of the
  equation
• 2 H2 1 O2 2 H2O
• H 2 4 H 4
• O 2 2 O 2

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LETS PRACTICE!!!

• __CH4 __ O2 __CO2 __H2O
• __Al __Br2 __AlBr3

22
LETS PRACTICE!!!

• 1 CH4 2 O2 1CO2 2 H2O
• 2 Al 3 Br2 2 AlBr3

23
LETS PRACTICE!!!

• _SrCl2 _KNO3 __ Sr(NO3)2_KCl
• __KOH __H2SO4 __K2SO4 __H2O

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LETS PRACTICE!!!

• 1 SrCl2 2 KNO3 1 Sr(NO3)22 KCl
• 2 KOH 1 H2SO4 1 K2SO4 2 H2O

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LETS PRACTICE!!!

• __H2O __N2O3 __HNO2
• __Fe __H2O __Fe3O4 __H2

26
LETS PRACTICE!!!

• 1 H2O 1 N2O3 2 HNO2
• 3 Fe 4 H2O 1 Fe3O4 4 H2

27
LETS PRACTICE!!!

• __C12H22O11 __H2O __C __H2O
• __Na2(SO4) __BaCl2 __BaSO4__NaCl

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LETS PRACTICE!!!

• 1 C12H22O11 1 H2O 12 C 12 H2O
• 1 Na2(SO4) 1 BaCl2 1 BaSO4 2 NaCl

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LETS PRACTICE!!!

• __PbO2 __PbO __O2
• __Cl2 __KBr __KCl __Br2

30
LETS PRACTICE!!!

• 2 PbO2 2 PbO 1 O2
• 1 Cl2 2 KBr 2 KCl 1 Br2

31
LETS PRACTICE!!!

• __NaCl __H2(SO4) __Na2SO4 __HCl

32
LETS PRACTICE!!!

• 2 NaCl 1 H2(SO4) 1 Na2SO4 2 HCl

33
Ratios Chemical Equations

• Ratios are written
• Use the Co-efficients when writing ratios
• 2 H2 1 O2 2 H2O
• RATIO FOR THIS EQUATION
• 212

34
QUESTION

• If I have 10 molecules of O2, how many molecules
  of H2O do I have?
• 2 H2 1 O2 2 H2O
• RATIO FOR THIS EQUATION
• 212

35
ANSWER

• If I have 10 molecules of O2, how many molecules
  of H2O do I have?
• 2 H2 1 O2 2 H2O
• RATIO FOR THIS EQUATION
• 2 1 2
• Oxygen Coefficient 10/1 10 molecules
• Water Coefficient 210 20 Molecules

36
QUESTION

• If I have 30 molecules of H2O, how many molecules
  of O2 do I have?
• 2 H2 1 O2 2 H2O
• RATIO FOR THIS EQUATION
• 212

37
ANSWER

• If I have 30 molecules of H2O, how many molecules
  of O2 do I have?
• 2 H2 1 O2 2 H2O
• RATIO FOR THIS EQUATION
• 2 1 2
• Water 30 molecules/2 15
• Oxygen 115 15 Molecules

38
QUESTION

• If I have 24 molecules of PbO, how many molecules
  of Pb do I have?
• PbS 2 PbO 3 Pb SO2
• RATIO FOR THIS EQUATION
• __ __ __ __

39
ANSWER

• If I have 24 molecules of PbO, how many molecules
  of Pb do I have?
• PbS 2 PbO 3 Pb SO2
• RATIO FOR THIS EQUATION
• 1 2 3 1
• PbO 24 molecules/2 12
• Pb 312 36 Molecules

40

• End notes for Thursday, November 2, 2006

41
Types of Chemical Reactions

• Synthesis Reaction
• Decomposition Reaction
• Single Displacement Reaction
• Double Displacement Reaction
• Combustion Reaction

42
Synthesis Reactions

• Addition reaction
• Two or more substances chemically combine to form
  ONE product
• A B C
• 4Al 3O2 2Al2O3
• 4Fe 3O2 2Fe2O3

43
Decomposition Reactions

• Breakdown Reaction
• ONE reactant breaks down into two or more
  substances
• AB A B
• 2KClO3 2KCl 3O2
• 2NaH(CO3) 2Na(CO3) H2

44
Single Displacement Reactions

• One ELEMENT replaces another in a compound
• A BC AC B
• Ca 2Ag(NO3) 2Ag Ca(NO3)2
• Fe CuCl2 FeCl2 Cu

45
Double Displacement Reactions

• The CATION of one compound replaces the CATION of
  another compound
• TWO compounds produce two NEW COMPOUNDS
• Usually produces a PRECIPITATE (something not
  soluble in water) a liquid/gas
• AB CD AD CB
• HCl NaF HF NaCl
• NaCl KBr NaBr KCl

46
Combustion Reactions

• A CARBON compound combines with OXYGEN to form
  CARBON DIOXIDE and WATER
• CARBON
• COMPOUND O2 CO2 H2O
• CH4 2O2 2H2O CO2

47
Energy in Reactions

• Energy is released or absorbed in ALL chemical
  reactions
• When bonds are FORMED, energy is RELEASED
• When bonds are BROKEN, energy is ABSORBED (Taken
  In)

48
Exothermic Reactions

• Energy is RELEASED
• Usually occurs in the form of HEAT because BONDS
  ARE BROKEN
• More bonds are FORMED than broken

49
Exothermic Reactions

• Energy will be on the PRODUCT side of the
  chemical equation
• Temperature Rises (Feels Warmer)
• Examples
• Burning of Gasoline
• Heat Packs
• Explosion of Dynamite

50
Endothermic Reactions

• Energy is ABSORBED (Taken in)
• More bonds are BROKEN than formed
• Temperature Drops (Feels Cold)
• Energy is on the REACTANT side of the chemical
  equation
• Examples
• Ice pack

51
Chemical Reactions in the Air

• Chlorofluorocarbons (CFCs)
• Released into the atmosphere through the use of
  air conditioners, forest fires, volcanos, and
  other daily activities
• Once released, CFCs decompose and yield Chlorine
  atoms, which destroy the ozone layer
• CF2Cl2 CF2 Cl2