Chemical Equations and Reactions

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Chemical Equations and Reactions

• Chapter 8

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Chemical Reactions

• Def process in which one or more substances are
  changed into new substances
• Start w/ REACTANTS and make PRODUCTS
• Law of Conservation of Mass mass of reactants
  must mass of products

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Chemical Equations

• Def uses symbols and formulas to represent
  identities of molecular or molar amts of a rxn
• 2H2(g) O2(g) ? 2H2O(l)

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Indications of Rxn

1. Evolution of heat and energy as light
2. Production of Gas (bubbles)
3. Formation of precipitate (insoluble compound)
4. Color change

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Chemical Equations

• Word Equations
• Calcium Oxygen ? Calcium oxide
• Formula Equations
• Ca O2 ? CaO
• Remember HONClBrIF only for LONE element
• Balance Charges when needed

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Symbols
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Symbols
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Complete Chemical Eqn

• BaCl2(aq) Na2CrO4(aq) ? BaCrO4(s) 2NaCl(aq)
• Formulas, Phases, Balanced
• 2Ca(s) O2(g) ? 2CaO(s)
• Solid sodium oxide is added to water and forms
  sodium hydroxide (dissolved in water).

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Balancing Equations
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Balancing Equations

• Making a bicycle?
• 4 major parts ?
• Frame wheel handlebar pedal ? bicycle
• 1 Frame (F) 2 Wheels (W)
• 1 Handlebar (H) 2 Pedals (P)

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Balancing Equations

• Bicycle
• FW2HP2
• Equation
• F W H P ? FW2HP2
• Unbalanced ? Balance it!
• F 2W H 2P ? FW2HP2

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Balancing Equations

• H2 O2 ? H2O
• Count of atoms on each side of equation
• Can only change COEFFICIENTS!!
• Coefficients are in lowest whole ratio
• If can, treat polyatomic ions as one unit
• If equation isnt balancing equation is WRONG!

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Balancing Equations

• FeCl2 Na3PO4 ? NaCl Fe3(PO4)2
• Al O2 ? Al2O3
• Li H2O ? LiOH H2

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Types of Reactions
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Types of Reactions

1. Synthesis (combination)
2. Decomposition
3. Single-Displacement
4. Double-Displacement
5. Combustion

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1. Synthesis Reactions

• Two or more reactants form ONE product
• A X ? AX
• 2Ca O2 ? 2CaO
• CO2 H2O ? H2CO3

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2. Decomposition Reactions

• ONE compound broken down into two or more smaller
  parts
• Reverse of combination
• AX ? A X
• Decomposition usually requires something electric
  ? electrolysis, heat, catalyst, etc.
• Ca(OH)2 ? CaO H2O
• 2KClO3 ? 2KCl 3O2

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3. Single-Displacement Rxns

• A single element replaces another element in a
  compound
• A BX ? AX B
• Y BX ? BY X
• BX and AX are generally IONIC compounds ? A and
  B are elements

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Activity Series

• A MORE reactive metal will REPLACE a less
  reactive metal
• Pg. 286
• metals replace metals or H
• nonmetals replace nonmetals
• Cl2 KI ? ?
• Zn H2O ?

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4. Double-Replacement Rxns

• Atoms or ions from two different compounds
  replace each other
• AX BY ? AY BX
• X and Y switch
• CaCO3 2HCl ? CaCl2 H2CO3
• HNO3 Ca(OH)2 ?

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5. Combustion Rxns

• Substance combines with O2 releasing large amts
  of heat and light
• (C-H) Compound O2 ? CO2 H2O
• Similar to combination rxn
• CH4 O2 ?

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Predict the Products

• Synthesis of Aluminum oxide from its elements.
• Combustion of ethane, C2H6
• Decomposition of calcium oxide to its elements

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Reaction Rates
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Rate-Influencing Factors

• Collision Theory reactions occur because of
  collisions between particles
• Inc. rate of reaction inc. collisions
• Surface Area
• Temperature
• Concentration
• Catalyst