Chemical Reactions

1
Chapter 7

• Chemical Reactions

2
Objectives

• Explain what a chemical reaction is
• Describe indications of chemical reactions
• Use state symbols in reactions
• Write balanced chemical equations

3
What is a Chemical Reaction?

• One or more substances are converted into new
  substances
• New substances
• must be formed!!!

4
All Chemical Reactions

• have two parts
• Reactants - the substances you start with
• Products- the substances you end up with
• The reactants turn into the products.
• Reactants Products

5
Indications of Reactions

• Change in Heat
• - Exothermic or Endothermic Reactions
• Light
• Production of a Gas Does not need to smell
• Formation of a Precipitate
• -Precipitate is a solid that is produced as a
  result of a chemical rxn in solution

6
Precipitate!
7
In a Chemical Reaction

• The way atoms are joined is changed
• Atoms arent created of destroyed.
• Can be described several ways
• In a sentence
• Copper reacts with chlorine to form copper (II)
  chloride.
• In a word equation
• Copper chlorine copper (II) chloride

8
Chemical Equation

• Represents with symbols and formulas, the
  identities and relative amounts of the reactants
  and products in a chemical rxn.

9
Symbols In Equations

• An arrow separates the reactants from the
  products
• Read reacts to form or yields
• The plus sign and
• (s) solid
• (g) gas
• (l) liquid
• (aq) aqueous solution
• Dissolved in water

10
Symbols In equations

• reversible reactions
• Equilibrium (More later)
• Reaction is heated
• Catalyst is used (Copper)
• Catalysts speed up reactions but are not
  consumed.
• Enzymes are biological catalysts
• Specific Pressure
• 2.00 atmospheres (1 atm is normal)

11
How Do Reactions Happen?

• Simple View
• Particles must collide

12
Reactions Continued

• Particles are moving (Kinetic Energy)
• -Higher temperature means a higher speed
• Particles collide
• -Energy is absorbed by particles
• -Bonds are broken
• -New bonds are formed
• -Energy is released

13
Diatomic Elements

• 7 elements ALWAYS exist in diatomic state
• Diatomic 2 atoms
• H2 , N2 , O2 , F2 , Cl2 , Br2 , I2
• Elements in ogen and ine
• 1 7 pattern on the periodic table

14
Diatomic Elements
15
Converting To Formula Equ.

• You will often have to convert word equations to
  formula equations.
• Determine the reactants and products
• Covert the words to equations
• Include any state symbols that are given
• If no state are given dont worry about them.

16
Converting To Formula Equ.

• Sodium metal and chlorine gas react to form solid
  sodium chloride

17
Converting To Formula Equ.

• A solution of hydrochloric acid and solid sodium
  carbonate react to form solid sodium chloride and
  gaseous carbon dioxide and water vapor.

18
Convert To a Sentence

• Fe(s) O2(g) Fe2O3(s)
• Solid Iron and gaseous oxygen yields solid iron
  (III) oxide

19
Convert To a Sentence

• Cu(s) AgNO3(aq) Ag(s) Cu(NO3)2(aq)
• Solid Copper and a solution of silver nitrate
  yields solid silver and a solution of copper (II)
  nitrate

20
Balanced Equation

• Law of Conservation of Mass states Mass cannot
  be created or destroyed.
• Thus, atoms cant be created or destroyed
• So, a balanced equation has the same number of
  each element on both sides of the equation.
• Balance equations with coefficients
• Number in front of a formula (Multiplier)

21
Is This Equation Balanced?
H2 I2 ? HI
22
NO WAY!

• Hydrogen and Iodine 2 reactant atoms only 1
  product atom

23
Balance With Coefficients

• If there are 2 HI molecules the equation is
  balanced. H2 I2 ? 2HI

24
Dont Change the Formula

• You make a different compound!!!!!

25
Writing Balanced Equations

1. Write the correct formulas for all the reactants
   and products
2. Count the number of atoms of each type appearing
   on both sides
3. Balance the elements one at a time by adding
   coefficients (the numbers in front)
4. Check to make sure it is balanced.

26
Never

• Never change a subscript to balance an equation.
• If you change the formula you are describing a
  different reaction.
• H2O is a different compound than H2O2
• Never put a coefficient in the middle of a
  formula
• 2 NaCl is okay, Na2Cl is not.

27
Examples

• H2 O2 ? H2O

28
Examples

• Ca(NO)3 NaI ? CaI2 NaNO3

29
Examples

• C2H6 O2 ? CO2 H2O

30
Homework

• p. 264 23,25,26,28,30-33

31
Objectives

• Predict a reaction type
• Predict the products of a reaction
• Use the activity series
• Predict solubility of compounds

32
Types of Reactions

• Predicting the Products

33
Types of Reactions

• There are millions of reactions.
• Cant remember them all
• Fall into several categories.
• We will learn 5 types.
• Will be able to predict the products.
• For some we will be able to predict whether they
  will happen at all.
• Will recognize them by the reactants

34
1 Synthesis Reactions

• Combine - put together
• 2 elements, or compounds combine to make one
  compound.
• Ca O2 CaO
• SO3 H2O H2SO4
• We can predict the products if they are two
  elements.
• Mg N2 Mg3N2

35
2 Decomposition Reactions

• decompose fall apart
• one reactant falls apart into two or more
  elements or compounds.
• NaCl Na Cl2
• CaCO3 CaO CO2

36
3 Single Replacement

• One element replaces another
• Reactants must be an element and a compound.
• Products will be a different element and a
  different compound.
• Na KCl K NaCl
• F2 LiCl LiF Cl2

37
3 Single Replacement

• We can tell whether a reaction will happen
• Some are more active than other
• More active replaces less active
• Higher on the list replaces lower.
• If the element by itself is higher, it happens,
  in lower it doesnt

38
Activity Series

• Lithium
• Potassium
• Calcium
• Sodium
• Magnesium
• Aluminum
• Zinc
• Chromium
• Iron
• Nickel
• Lead
• Hydrogen
• Bismuth
• Copper
• Mercury
• Silver
• Platinum
• Gold

• Halogens -
• F2
• Cl2
• Br2
• I2

39
3 Single Replacement

• What does it mean that Au And Ag are on the
  bottom of the list?
• Nonmetals can replace other nonmetals
• Limited to F2 , Cl2 , Br2 , I2
• The order of activity is that on the table.
• Higher replaces lower.

40
Solubility

• Some compounds dissolve in water.
• We say they are Soluble
• Examples
• Sodium Chloride, Potassium Nitrate
• Some compounds do not dissolve
• We say they are Insoluble
• Form Precipitates

41
Solubility Rules

• Solubility Rules are a general list that tells us
  what kind of compounds are soluble or insoluble.
• Follow from beginning to end
• Rule one has precedence over rule two

42
Solubility Rules

• All Acids are soluble
• Most nitrate and acetate salts are soluble.
• Most salts containing the alkali metal ions (Li,
  Na, K, Cs, Rb) and the ammonium (NH4) ion
  are soluble.
• Most chloride, bromide and iodide salts are
  soluble. Exceptions are salts containing the ions
  Ag, Pb2, and Hg2.
• Most sulfate salts are soluble. Notable
  exceptions are BaSO4, PbSO4, HgSO4 and CaSO4.

43
Solubility Rules

• Most hydroxide salts are insoluble.
• Most sulfide (S2-), carbonate (CO32-), chromate
  (CrO42-) and phosphate (PO43-) salts are
  insoluble

44
Solubility Rules

• M I Soluble?
• Potassium Bromide
• Yes
• Iron (III) Sulfate
• Yes
• Calcium Phoshate
• No
• Zinc Acetate
• Yes

45
4 Double Replacement

• Two things replace each other.
• Reactants must be two ionic compounds or acids.
• Usually in aqueous solution
• NaOH FeCl3 Fe(OH)3 NaCl

46
4 Double Replacement

• Will only happen if one of the products
• doesnt dissolve in water and forms a solid
• or is a gas that bubbles out.
• or is a covalent compound usually water.

47
Examples

• H2 O2
• H2O
• Zn H2SO4
• HgO
• KBr Cl2
• AgNO3 NaCl
• Mg(OH)2 H2SO3

48
Last Type

• Combustion
• A compound composed of only C H and maybe O is
  reacted with oxygen
• If the combustion is complete, the products will
  be CO2 and H2O.
• CH4 O2 ? CO2 2H2O

49
How to recognize which type

• Synthesis Only one product
• Decomposition Only one reactant
• Single replacement Element and Compound as
  reactants
• Double replacement Two compounds
• Combustion Something reacting with oxygen

50
Homework

• p. 264 's 35 37-40, 46 without net ionic

51
Objectives

• Predict the type of double replacement reaction
• Write net ionic equations

52
More on Double Replacement

• Three Main Types
• Precipitation (A solid forms)
• Gas Forming (A gas forms)
• Neutralization
• Reaction of Acid and Base

53
Precipitation

• One of the products will be a solid
• Determined by solubility rules
• Thats it.

54
Gas Forming

• You see bubbles!
• Usually from decomposition of
• Carbonic Acid - H2CO3 ? CO2 H2O
• Sulfurous Acid - H2SO3 ? SO2 H2O
• When you get one of these as a product replace it
  with the gas and water.
• Ex. HNO3 Na2CO3 ? H2CO3 NaNO3
• Products become CO2 H2O NaNO3

55
Neutralization

• Reaction of Acid and a Base
• Acid usually starts with H
• Base usually has hydroxide OH-
• Product is salt and water
• Ex HF KOH? HOH KF

56
Dissociation

• Ionic Compounds separating into ions
• AgNO3(aq)Na2S(aq)?Ag NO3- 2Na S-2

57
Net Ionic Equations

• Used to remove unimportant reactants and
  products
• Whats unimportant
• Whatever is not used to make precipitates,
  liquids, or gases
• They are spectator ions

58
Net Ionic Rules

• Dissociate all soluble compounds
• According to balanced equation
• Leave all solids, liquids, and gasses
• Cross out common terms (Same)
• Rewrite as net ionic

59
Example

• Solutions of lead (II) nitrate hydrochloric
  acid are in beakers. Draw what in is in the
  beakers.

60
Example

• Solutions of lead (II) nitrate hydrochloric
  acid are mixed. Write the balanced equation

61
Example

• Draw what is in the beaker when the two solutions
  are mixed.

62
Example

• Solutions of lead (II) nitrate hydrochloric
  acid are mixed. Write the net ionic equation

63
Example

• Solutions of copper (II) nitrate and sodium
  sulfide are mixed. Write the net ionic equation.

64
Homework

• p. 266 's 46,62ab,68,75,82,98