CHAPTER 8 CHEMICAL REACTIONS

1
CHAPTER 8CHEMICAL REACTIONS

• LEARNING THE PATTERNS OF CHEMICAL REACTIONS

2
INTRODUCTIONSection 8.1 Describing Chemical
Change

• A. What is a CHEMICAL EQUATION?
• B. Why must an equation be balanced?

3
INTRODUCTIONSection 8.1 Describing Chemical
Change

• A. What is a CHEMICAL EQUATION?
• A chemical sentence that describes chemical
  changes.
• B. Why must an equation be balanced?
• to obey the law of conservation of mass
• mass of reactants must equal mass of products

4
C. 5 TYPES OF CHEMICAL REACTIONS

• 1. Combination (synthesis)
• A B ? AB
• 2 reactants ? 1 Product
• (each just 1 element) (a compound)
• (monatomic or diatomic)
• Example
• 2H2 O2 ? 2H2O

5
C. 5 TYPES OF CHEMICAL REACTIONS

• 1. Combination (synthesis)
• A B ? AB
• 2. Decomposition
• AB ? A B
• 1reactant ? 2 Products
• (a compound) (each just elements)

6
C. 5 TYPES OF CHEMICAL REACTIONS

• 3. Single Replacement
• A BC ? AC B
• (A metal) metal, A, bonds with anion C
• X YZ ?YX Z
• (X nonmetal) nonmetal, X, bonds with cation Y

7
C. 5 TYPES OF CHEMICAL REACTIONS

• 4. Double Replacement
• AB CD ? AD CB
• CATION FROM ONE COMPOUND REPLACES THE CATION FROM
  THE OTHERAND THE ANION
• FROM ONE WILL
• REPLACE THE ANION
• FROM THE OTHER.

8
C. 5 TYPES OF CHEMICAL REACTIONS

• 5. COMBUSTION (burning a hydrocarbon)
• CXHY O2 ? XCO2 y/2 H2O
• Combustion of Propane
• C3H8 5 O2 ? 3 CO2 4 H2O
• These are all examples of COMPLETE combustion

9
C. 5 TYPES OF CHEMICAL REACTIONS

• 5. COMBUSTION, continued
• During COMPLETE combustion, there is enough
  oxygen to completely burn off all the fuel the
  product is CO2.
• During INCOMPLETE combustion, CO is produced
  instead, since there is not enough oxygen
  available.

10
CHEMICAL EQUATIONS

• D. Define REACTANTS -
• starting substances
• E. Define PRODUCTS -
• ending substances
• Reactants ? products
• Reactants yield products

11
Table 8.1Symbols Used in EquationsUse your
textbook, page 206, to write the symbols for the
following words/phrases

• yields
• precipitate is made
• a gas is produced
• heat is being applied
• a catalyst is used
• a reversible reaction

• solids
• liquids
• gases
• aqueous
• heat

It would be in your best interest to commit these
symbols and their meanings to memory.
12
DEFINITIONS

• G. What is a skeleton equation?
• not balanced yet
• H. What is a catalyst?
• a substance that speeds up a reaction without
  being used up.

13
Practice Problems

• Write a skeleton equation for each of these
  chemical reactions
• 1. Aluminum metal reacts with oxygen in the air
  to form aluminum oxide.
• 2. When solid mercury (II) sulfide is heated with
  oxygen, liquid mercury metal and gaseous sulfur
  dioxide are produced
• 3. Oxygen gas can be made by heating potassium
  chlorate in the presence of the catalyst
  manganese dioxide. Potassium chloride is left as
  a solid residue..

14
Practice Problems

• Write a skeleton equation for each of these
  chemical reactions
• 1. Aluminum metal reacts with oxygen in the air
  to form aluminum oxide.

15
Practice Problems

• Write a skeleton equation for each of these
  chemical reactions
• 1. Aluminum metal reacts with oxygen in the air
  to form aluminum oxide.

16
Practice Problems

• Write a skeleton equation for each of these
  chemical reactions
• 2. When solid mercury (II) sulfide is heated with
  oxygen, liquid mercury metal and gaseous sulfur
  dioxide are produced

17
Practice Problems

• Write a skeleton equation for each of these
  chemical reactions
• 2. When solid mercury (II) sulfide is heated with
  oxygen, liquid mercury metal and gaseous sulfur
  dioxide are produced

18
Practice Problems

• Write a skeleton equation for each of these
  chemical reactions
• 3. Oxygen gas can be made by heating potassium
  chlorate in the presence of the catalyst
  manganese dioxide. Potassium chloride is left as
  a solid residue..

19
Practice Problems

• Write a skeleton equation for each of these
  chemical reactions
• 3. Oxygen gas can be made by heating potassium
  chlorate in the presence of the catalyst
  manganese dioxide. Potassium chloride is left as
  a solid residue..

20

• Write sentences that completely describe each of
  the chemical reactions shown in these skeleton
  equations.
• KOH(aq) H2SO4 (aq) ? H2O(l) K2SO4(aq)
• Na(s) H2O(l) ? NaOH(aq) H2(g)

21

• Write sentences that completely describe each of
  the chemical reactions shown in these skeleton
  equations.
• KOH(aq) H2SO4 (aq) ? H2O(l) K2SO4(aq)
• When potassium hydroxide, in aqueous solution
  combines with aqueous sulfuric acid, the result
  is liquid water and a potassium sulfate solution.
  
• Na(s) H2O(l) ? NaOH(aq) H2(g)

22

• Write sentences that completely describe each of
  the chemical reactions shown in these skeleton
  equations.
• KOH(aq) H2SO4 (aq) ? H2O(l) K2SO4(aq)
• When potassium hydroxide, in aqueous solution
  combines with aqueous sulfuric acid, the result
  is liquid water and a potassium sulfate solution.
  
• Na(s) H2O(l) ? NaOH(aq) H2(g)
• Solid sodium in liquid water yeilds a solution of
  sodium hydroxide and hydrogen bubbles.

23
Balancing equations

• Remember, in a chemical reaction, atoms are not
  created or destroyed, but simply rearranged.
• In every balanced equation, each side of the
  equation has the same number of atoms of each
  element.

24
Rules for Balancing Equationsfrom pg. 208-209

• 3. Count the number of atoms of each element in
  the reactants and products.
• 4. If a polyatomic ion appearing unchanged on
  both sides of the equation is counted as a single
  unit.

• 1. Determine the correct formulas for all the
  reactants and products in the reaction.
• 2. Write the formulas for the reactants on the
  left and the formulas for the products on the
  right with an arrow in between. If two or more
  reactants or products, separate them with a sign

25
Rules Cont

• 5. Balance the elements one at a time using
  coefficients. NEVER CHANGE A SUBSCRIPT TO
  BALANCE AN EQUATION!!!!!

• CHECK EACH ATOM OR POLYATOMIC ION TO BE SURE THAT
  THE EQUATION IS BALANCED
• 6. MAKE SURE COEFFICIENT RATIO IS LOWEST
  POSSIBLE RATIO.

26
PRACTICE BALANCING

• PROBLEM 3 PG 209

• PROBLEM 4 PG 209