Bell Work

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Bell Work

• Define the terms to learn on page 541. Turn them
  into the black wire basket when finished.

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Chapter 20 Section 3

• Energy and Rates of Chemical Reaction

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Classifying Reactions in Terms of Energy
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Exothermic Reactions

• A reaction in which energy is released or removed
  is called an exothermic reaction.

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Exothermic Reactions

• Energy is released because the chemical energy of
  the reactants is greater than the chemical energy
  of the products.

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Exothermic Reactions

• Exo means go out or exit
• Thermic means heat or energy

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Endothermic Reactions

• A reaction in which energy is absorbed is called
  and endothermic reaction.

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Endothermic Reactions

• This happens because the energy of the products
  is greater than the energy of the reactants.

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Endothermic Reactions

• Endo means go in
• Thermic means heat or energy

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Writing Exothermic and Endothermic Reaction
Equations
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Exothermic Reactions

• 2Na Cl2 --gt 2NaCl energy

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Endothermic Reactions

• 2H2O energy --gt 2H2 O2

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Energy is Conserved Its a Law!

• The Law of Conservation of Energy states that
  energy can neither be created nor destroyed.

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How Much Energy Does It Take to Start a Chemical
Reaction?
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Activation Energy

• The minimum amount of energy needed for
  substances to react is called activation energy.
• This is different for every reaction!

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Activation Energy

• Examples friction when striking a match causes
  it to burn or electrical spark in a cars
  ignition begins the burning of gasoline

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Factors Affecting Rates of Reaction
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4 Factors That Affect Reaction Rates

• Temperature
• Concentration
• Surface Area
• Catalysts and Inhibitors

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Temperature

• An increase in temperature increase the rate of a
  reaction. (speeds it up)

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Temperature

• This happens because at higher temperatures the
  particles in the reactants move faster and
  collide with each other more often and with more
  energy.

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Concentration

• Concentration is a measure of the amount of one
  substance dissolved in another.
• Increasing the concentration increases the number
  of reactant particles and decreases the distance
  between them.

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Surface Area

• Increasing the surface area, or the amount of
  exposed surface, of solid reactants increases the
  rate of reaction.
• Grinding a solid into a powder is a good way to
  do this!

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Catalysts

• A catalyst is a substance that speeds up a
  reaction without being permanently changed.
• A catalyst lowers the activation energy of a
  reaction allowing it to occur more quickly.

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Inhibitors

• An inhibitor is a substance that slows down or
  stops a reaction.
• Preservatives slow down the spoiling of food.

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Questions?
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Homework

• Read Chapter 20 Sections and 3
• Complete workbook pages for section 3 pages
  160,161,162