Chapters 8, 17, and 18

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UNIT 5Chemical Reactions, Rates, and Equilibrium

• Chapters 8, 17, and 18

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Chemical Equations and Reactions
Chapter 8
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What Is a Chemical Reaction?
Chapter 8 Section 1 Describing Chemical
Reactions

• A chemical reaction is the process by which one
  or more substances are changed into one or more
  different substances.
• In any chemical reaction, the original substances
  are known as the reactants and the resulting
  substances are known as the products.

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The Law of Conservation of Mass
Chapter 8 Section 1 Describing Chemical
Reactions

• According to the law of conservation of mass, the
  total mass of reactants must equal the total mass
  of products for any given chemical reaction.

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Indications of a Chemical Reaction
Chapter 8 Section 1 Describing Chemical
Reactions

• Signs that a chemical reaction is taking place
• Release of energy as heat and/or light.
• Production of a gas.
• Formation of a precipitate.
• Precipitate - a solid that separates from a
  liquid solution.
• Color change.

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Chemical Equations
Chapter 8 Section 1 Describing Chemical
Reactions

• A chemical equation represents a chemical
  reaction using symbols and formulas.
• Example

2H2O(l) 2H2(g) O2(g)
Products
Reactants
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Rules for Writing Chemical Equations
Chapter 8 Section 1 Describing Chemical
Reactions

1. The equation must represent known facts.
2. The equation must contain the correct formulas
   for the reactants and products.
3. The law of conservation of mass must be satisfied.

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Word Equations
Chapter 8 Section 1 Describing Chemical
Reactions

• The first step in writing a chemical equation is
  to identify the facts.
• In a word equation the reactants and products
  are represented by words.
• A word equation is qualitative.
• Example
• methane oxygen carbon dioxide water

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Formula Equations
Chapter 8 Section 1 Describing Chemical
Reactions

• The next step is to replace the names of the
  reactants and products with symbols and formulas.
• A formula equation represents the reactants and
  products of a chemical reaction by their symbols
  or formulas.
• Example
• CH4(g) O2(g) CO2(g) H2O(g)

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Diatomic Molecules
Chapter 8 Section 1 Describing Chemical
Reactions

• Oxygen gas (O2) is an example of an element that
  normally exists as a diatomic molecule. You need
  to memorize all seven

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Symbols used in Chemical Equations
Chapter 8 Section 1 Describing Chemical
Reactions
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Word and Formula EquationsSample Problem
Chapter 8 Section 1 Describing Chemical
Reactions

• Write word and formula equations for the
  reaction that occurs when solid copper metal
  reacts with aqueous silver nitrate to produce
  solid silver metal and aqueous copper(II)
  nitrate.
• Solution
• Word Equation
• Formula Equation (not balanced)

?
copper

silver nitrate
silver
copper(II) nitrate

? Ag(s)
Cu(s)
AgNO3(aq)
Cu(NO3)2(aq)
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Balancing Equations
Chapter 8 Section 1 Describing Chemical
Reactions

• The final step in writing correct chemical
  equations is to make sure the law of conservation
  of mass is satisfied.
• The numbers and types of atoms on both sides of
  the equation must be the same this is called
  balancing an equation.
• Equations are balanced by inserting coefficients
  - whole numbers that appear in front of formulas
  in a chemical equation.

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Balancing EquationsSample Problem A
Chapter 8 Section 1 Describing Chemical
Reactions

• Balance the following equation CH4(g)
  O2(g) CO2(g) H2O(g)
• Solution
• Start with the easiest elementcarbon.
• Carbon is already balanced.
• Next count the hydrogen atoms.
• Two more hydrogen atoms are needed on the right.
• Finally, count oxygen atoms.
• There are 4 oxygens on the right side of the
  equation, but only two on the left.
• Add a coefficient 2 in front of the O2 on the
  left.

2
2
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Balancing EquationsSample Problem B
Chapter 8 Section 1 Describing Chemical
Reactions

• Balance the following equation Al4C3(s)
  H2O(l) CH4(g) Al(OH)3(s)
• Solution
• Lets start with aluminum.
• Add a coefficient 4 to Al(OH)3 on the right.
• Next count the carbon atoms.
• Add a coefficient 3 to CH4 on the right.
• Balance the oxygen atoms.
• Add a 12 to the H2O on the left.
• Lastly, count the hydrogen atoms.
• Hydrogen is already balanced.

3
4
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Types of Chemical Reactions
Chapter 8 Section 2 Types of Chemical Reactions

• There are 5 basic types of chemical reactions
• Synthesis
• Decomposition
• Single-Displacement
• Double-Displacement
• Combustion

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Synthesis Reactions
Chapter 8 Section 2 Types of Chemical Reactions

• In a synthesis reaction (also called a
  composition reaction) 2 or more substances
  combine to form a new compound.
• This type of reaction is represented by the
  following general equation
• A X AX

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Synthesis - Examples
Chapter 8 Section 2 Types of Chemical Reactions

• 2Mg(s) O2(g) 2MgO(s)
• S8(s) 8O2(g) 8SO2(g)
• 2H2(g) O2(g) 2H2O(g)
• 2Na(s) Cl2(g) 2NaCl(s)
• Mg(s) F2(g) MgF2(s)

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Decomposition Reactions
Chapter 8 Section 2 Types of Chemical Reactions

• In a decomposition reaction, a single compound
  breaks apart to form 2 or more simpler
  substances.
• Decomposition is the opposite of synthesis.
• This type of reaction is represented by the
  following general equation
• AX A X

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Decomposition - Examples
Chapter 8 Section 2 Types of Chemical Reactions
electricity

• 2H2O(l) 2H2(g) O2(g)
• CaCO3(s) CaO(s) CO2(g)
• H2CO3(aq) CO2(g) H2O(l)
• 2HgO(s) 2Hg(l) O2(g)
• Ca(OH)2(s) CaO(s) H2O(g)

?
?
?
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Single-Displacement Reactions
Chapter 8 Section 2 Types of Chemical Reactions

• In a single-displacement reaction (also called
  single-replacement) one element replaces a
  similar element in a compound.
• They often take place in aqueous solution.
• This type of reaction is represented by the
  following general equation
• A BX AX B

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Single Displacement - Examples
Chapter 8 Section 2 Types of Chemical Reactions

• 2Na(s) 2H2O(l) 2NaOH(aq) H2(g)
• 3Fe(s) 4H2O(g) Fe3O4(s) 4H2(g)
• Mg(s) 2HCl(aq) H2(g) MgCl2(aq)
• Cl2(g) 2KBr(aq) 2KCl(aq) Br2(l)
• F2(g) 2NaCl(aq) 2NaF(aq) Cl2(g)

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Double-Displacement Reactions
Chapter 8 Section 2 Types of Chemical Reactions

• In double-displacement reactions, the ionsof 2
  compounds exchange places in an aqueous solution
  to form 2 new compounds.
• One of the compounds formed is usually either a
  precipitate, a gas, or water.
• Represented by the following general equation
• AX BY AY BX

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Double Displacement - Examples
Chapter 8 Section 2 Types of Chemical Reactions

• Formation of a Precipitate
• 2KI(aq) Pb(NO3)2(aq) PbI2(s) 2KNO3(aq)
• Formation of a Gas
• FeS(s) 2HCl(aq) H2S(g) FeCl2(aq)
• Formation of Water
• HCl(aq) NaOH(aq) NaCl(aq) H2O(l)

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Combustion Reactions
Chapter 8 Section 2 Types of Chemical Reactions

• In a combustion reaction, a fuel combines with
  oxygen, releasing a large amount of energy in
  the form of light and heat.
• Products of combustion reactions are always
  carbon dioxide and water vapor.
• Example Combusion of propane
• C3H8(g) 5O2(g) 3CO2(g) 4H2O(g)

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Types of ReactionsSample Problem
Chapter 8 Section 2 Types of Chemical Reactions

• Classify each of the following reactions as a
  synthesis, decomposition, single-displacement,
  double-displacement, or combustion reaction.
• N2(g) 3H2(g) ? 2NH3(g)
• 2Li(s) 2H2O(l) ? 2LiOH(aq) H2(g)
• 2NaNO3(s) ? 2NaNO2(s) O2(g)
• 2C6H14(l) 19O2(g) ? 12CO2(g) 14H2O(l)

synthesis
single-displacement
decomposition
combustion
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Chemical Activity
Chapter 8 Section 3 Activity Series of the
Elements

• The ability of an element to react is referred to
  as the elements activity.
• The more easilyan element reactswith other
  substances, the greater its activity is.

Li
Au
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Activity Series
Chapter 8 Section 3 Activity Series of the
Elements

• An activity series is a list of elements
  organized by their chemical activity.
• The most-active element is placed at the top in
  the series.
• It can replace each of the elements below it in a
  single-displacement reaction.
• Activity series can be used to predict whether a
  chemical reaction will occur.
• Activity series are based on experiment.

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Activity Series (continued)
Chapter 8 Section 3 Activity Series of the
Elements
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Activity SeriesSample Problem
Chapter 8 Section 3 Activity Series of the
Elements

• Use the activity series to predict whether or not
  there will be a reaction for the possibilities
  below. If a reaction will occur, write the
  products and balance the equation.
• Ni(s) Pb(NO3)2(aq) ? ____
• MgCl2(aq) Zn(s) ? _____
• Br2(l) KI(aq) ? _____
• Cu(s) HCl(aq) ? _____

Pb(s) Ni(NO3)2(aq)
Yes
No reaction
2
I2(l) KBr(aq)
2
Yes
No reaction
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Reaction Kinetics Chemical Equilibrium
Chapters 17 18
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Collision Theory
Chapter 17 Section 1 The Reaction Process

• Collision Theory says that in order for
  reactions to occur between substances,
  particles must collide.
• For a collision to be effective, the particles
  must
• Collide with sufficient energy.
• Have a favorable orientation.

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Activation Energy
Chapter 17 Section 1 The Reaction Process

• Energy is needed to overcome the repulsion forces
  between molecules and transform the reactants
  into an activated complex.
• Activation energy is the minimum energy required
  to get a reaction started.

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Rate-Influencing Factors
Chapter 17 Section 2 Reaction Rate

• The rate of a chemical reaction depends on the
  number of collisions between particles.
• Rate-influencing factors are
• Nature of Reactants
• Surface Area
• Temperature
• Concentration
• Presence of Catalysts

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Reversible Reactions
Chapter 18 Section 1 The Nature of Chemical
Equilibrium

• A chemical reaction in which the products can
  react to re-form the reactants is called a
  reversible reaction.
• A reversible reaction is written using double
  arrows to show that the reaction is proceeding in
  both directions.
• Example

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Chemical Equilibrium
Chapter 18 Section 1 The Nature of Chemical
Equilibrium

• A reversible reaction is in chemical equilibrium
  when the rate of its forward reaction equals the
  rate of its reverse reaction and the
  concentrations of its products and reactants
  remain unchanged.
• At equilibrium, both reactions continue, but
  there is no net change in the composition of the
  system.