5'1 Nature of Chemical Reactions Objectives

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Chapter 5
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5.1 Nature of Chemical ReactionsObjectives

• Recognize some signs that a chemical reaction is
  taking place
• Explain chemical changes in terms of the
  structure and motion of atoms and molecules
• Describe the differences between endothermic and
  exothermic reactions
• Identify situations involving chemical energy

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Key Terms

• Reactant
• Product
• Chemical energy

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• Exothermic reaction
• Endothermic reaction

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What are some chemical reactions
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Chemical reactions change substances

• Production of gas and change of color are signs
  of chemical reactions
• What makes the bread rise?
• What is happening to the bonds?
• What makes it change color?
• Chemical reactions rearrange atoms
• Gas burning the products and reactants contain
  the same types of atoms C,H,O
• Atoms are rearranged conservation of mass

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Energy Reactions

• Energy must be added to break bonds
• Heat, electricity, sound, light
• When molecules collide, energy is transferred to
  separate atoms and bonds break
• Forming bonds releases energy
• Once there is enough energy new bonds form
• New bonds release of energy

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• Energy is conserved in chemical reactions
• Stored energy is chemical energy
• The total energy before the reaction is to the
  total energy of the products their surroundings
• TE Products surroundings

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• Reactions that release energy are exothermic
• After an exothermic reaction the temp. of the
  surrounding rise
• Reactions that absorb energy are endothermic
• More energy is needed to break the bonds in the
  reactants than is given off by forming bonds in
  the products
• May cause a temp. drop
• Energy, as heat, must sometimes be added to cause
  the reaction to take place

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5.2 Reaction TypesObjectives

• Distinguish among five general types of chemical
  reactions
• Predict the products of some reactions based on
  the reaction type
• Describe reactions that transfer or share
  electrons between molecules, atoms, or ions

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Key Terms

• Synthesis reaction
• Decomposition reaction
• Electrolysis
• Combustion reaction

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• Single-displacement reaction
• Double-displacement reaction
• Redox reaction
• Radical

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Classifying Reactions

• Synthesis reactions combine substances
• Polymerization small molecules join together in
  chains to make larger structures called polymers
• At least 2 reactants join to form a product
• General form A B AB
• 2Na Cl2 gt 2NaCl

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• Decomposition reactions break substances apart
• Substances are broken apart
• AB gt AB
• 2H2O gt 2H2 O2
• The electrolysis of water water breaks down
  when an electric current flows thru it
• Combustion reactions use oxygen as a reactant
• EX

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• In single-displacement reactions, elements trade
  places
• XA B gt BA X
• 3CuCl2 2Al gt 2AlCl3 3Cu
• Generally a more reactive element will take the
  place of a less reactive one
• In double-displacement reactions, compounds
  appear to exchange ions
• AX BY gt AY BX

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5.3 Balancing Chemical EquationsObjectives

• Demonstrate how to balance chemical equations
• Interpret chemical equations to determine the
  relative number of moles of reactants needed and
  moles of products formed
• Explain how the law of definite proportions
  allows for predictions about reaction amounts
• Calc. the relative masses of reactants products
  from a chemical equation

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Key Terms

• Chemical equation
• Mole ratio

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Describing Reactions

• Chemical equations summarize reactions
• The reactants on the left-hand side of the arrow
  form the products on the right side
• Balanced chemical equations acct. for the
  conservation of mass
• of atoms of ea. Element on the right side
  matches the of atoms of ea. Element on the left
• The total mass of the reactants is always the
  same as the total mass of products

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• How to balance chemical equations
• An equation can only be balanced by putting
  coefficients (numbers) in front of the chemical
  formulas
• Goal - of atoms for ea. element are the same on
  ea. side

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• The Law of Definite Properties
• A cmpd always contains the same elements in the
  same proportions, regardless of how the cmpd is
  made or how much of the cmpd is formed

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5.4 Rates of ChangeObjectives

• Describe the factors affecting the reaction rates
• Explain the effect a catalyst has on a chemical
  reaction
• Explain chemical equilibrium in terms of equal
  forward and reverse reaction rates
• Apply Le Chateliers principle to predict the
  effect of changes in concentration, temp,
  pressure in an equilibrium process

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Key Terms

• Catalyst
• Enzyme
• Substrate
• equilibrium

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• Le Chateliers principle

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Factors Affecting Reaction Rates

• For any reaction to occur, the particles of the
  reactants must collide with one another
• Most reactions go faster at higher temperatures
• Kinetic theory -

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• A large surface area speeds up reactions
• The surface area of a solid is the amt of the
  surface that is exposed
• Concentrated solutions react faster
• ex few drops of bleach in a lot of water wont
  affect clothes
• Whole bottle of bleach in washer will hurt the
  clothes
• The more concentrated solution has more bleach
  particles which means a higher chance for
  particle collisions with the clothes

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• Reactions are quicker at higher pressure
• A gas at high pressure is more concentrated than
  a gas at low pressure because the gas at high
  pressure has been squeezed into a smaller volume
• Massive, bulky molecules react slower
• Kinetic theory
• The molecules w/ more mass collide less often w/
  other molecules
• They react slowly because many unsuccessful
  collisions may occur before a reaction can begin

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• Catalysts change the rates of chemical reactions
• They speed up or slow down reactions
• Inhibitors catalysts that slow reactions
• Enzymes are biological catalysts
• Proteins are catalysts for chem. reactions in
  living things

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Equilibrium Systems

• Some changes are reversible
• Ex soda
• Equilibrium results when rates balance
• Ex soda
• Ex football team
• Systems in equilibrium respond to minimize change

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• Le Chateliers principle predicts changes in
  equilibrium
• If a change is made to a system it will work to
  come back to equilibrium
• General rule that describes the behavior of
  equilibrium systems
• Temperature increasing temp. favors the reaction
  that absorbs energy
• Pressure increasing pressure favors the reaction
  that produces less gas
• Concentration increasing the concentration of 1
  substance favors the reaction that produces less
  of that substance