Factors affecting the rate of reaction'

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Factors affecting the rate of reaction.

• Remember the molecules/compounds have to touch
  to react.

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1. Concentration

• Recall aqueous solutions. The substance is
  dissolved in water but water is not involved in
  the chemical change.
• If you increase the concentration you increase
  the number of molecules so the chance of
  interaction is greater.
• Therefore, the rate of reaction increases.

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2. Temperature

• If you increase the temperature you increase
  reaction rates.
• The molecules are moving faster so there is a
  greater chance of interaction between molecules
  or compounds.

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3. Surface Area

• If you wanted to sweeten your ice tea, would you
  add a packet of ground up sugar or a sugar cube?
• Hopefully, you would use the packet because a
  greater amount of the surface is exposed to the
  tea.
• Granted dissolving is a physical change but the
  same is true of a chemical change.
• If more of the surface area is exposed then the
  reaction will occur faster.

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4. Pressure

• If you increase the pressure you increase the
  reaction rates because a gas/molecules at higher
  pressure are more concentrated than gasses at
  lower pressures.
• Therefore, the have more collisions and
  interactions.

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5. Catalysts

• Catalysts are substances that help a reaction
  take place or speed up. They are not reactants or
  products.
• Many reactions would not take place without a
  catalysts.
• They work in different ways but generally reduce
  the amount of energy needed to start the
  reaction.
• Enzymes are special proteins that control the
  reaction rates of the chemical reactions that
  keep you alive.
• Ex Amylase protease

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Reversible reactions

• Some reactions are reversible. They are very
  similar to combining a synthesis and a
  decomposition reaction

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Reversible reactions

• Noted by arrows going both directions
• ?------- and -----? but they are on top of one
  another.
• When rate of the reaction is equal in each
  direction Equilibrium is reached.
• Le Chateliers Principle If a change is made to
  a system in chemical equilibrium, the equilibrium
  shifts to oppose the change until a new
  equilibrium is reached.

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Redox Reactions

• Reduction/oxidation reactions occur when
  electrons are transferred from one reactant to
  another.
• Important in industry
• Substances that accept electrons are said to be
  reduced.
• Substances that give up electrons are said to be
  oxidized.

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Radicals

• These are molecules with at least one unpaired
  electron.
• These often form when covalent molecules break
  apart.
• They consists of an uncharged hydrogen but react
  quickly to form new bonds.
• AKA free radicals

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Evidence a Chemical Change has Occurred

• Heat and light given off
• Color change
• Formation of a solid from 2 liquids that solid
  is called a precipitate
• Bubbling or fizzing
• Change in pH
• It is important to remember that this means a
  chemical change is likely.