RATE AND EXTENT OF REACTIONS

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RATE AND EXTENT OF REACTIONS
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• Rates or reactions (reaction kinetics)
• - The rate at which something occurs is an
  indication of the change of that particular
• entity per unit time (how fast or slow
  something is)
• - The reaction rate is the change in the
  CONCENTRATION of the reactants and products
• PER UNIT TIME (unit mol.dm-3.s-1)
• During a reaction
• Reactants ? Products
• - the concentration of the reactants will
  decrease, while that of the products increase
• - The average speed of a reaction can be found
  by considering the change in the
• concentration of the reactants or products

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Collision theory - Reactions occur when 2/more
reactant particles collide to form product
particles - As a result of collisions, bonds can
be broken and atoms in the particles rearranged -
The more collisions per second, the faster the
reaction - Not all collisions result in a
reaction, only effective collisions - Factors
that need to be considered 1) Correct
orientation of molecules 2) Energy of the
molecule - Not all molecules, in a
mixture at a specific temperature will have
enough KE to break bonds on collision
with other particles - Distribution of
the KE of the molecules in a mixture is given by
the following - No molecules with zero
KE - Always a fraction of molecules
with very high KE - The peak indicates the
most probable energy of most
molecules - The area below the curve gives
the total number of molecules in the
system
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• - For a reaction to occur, the molecules must
  have more energy than the activation energy
• EA Minimum Kinetic energy needed to let the
  reaction occur
• Summary of collision theory
• 5 Factors that influence the reaction rate and
  collision theory
• 1) The nature of the reactants
• - The strength of the bonds between
  reactant molecules differ
• - Thus the activation energy is related to
  bond strength
• 2) Concentration
• - If the concentration of the reactants is
  increased
• - There are more particles present
• - Thus more reactions take place per
  second
• - Thus a higher proportion of
  collisions have KE greater than the activation
  energy

http//www.youtube.com/watch?vkjKyEdrVXJAfeature
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http//www.youtube.com/watch?vJQdlQAwlTtgfeature
related
http//www.youtube.com/watch?vt0xl0CXjB04
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5) Adding a catalyst - A catalyst (a
substance that influences the rate of the
reaction without undergoing any permanent
change itself or being used up) is known as a
positive catalyst - A catalyst provides an
alternative (lower activation energy) route for
the reaction - It does this by providing a
new mechanism for the reactants to bond -
Catalysts can be solids, liquids or gasses
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Measuring the reaction rate - There are
different methods to enable us to calculate the
reaction rate - The method chosen, depends on
the properties of the particular reaction - For
example, when a gas is formed (product), the rate
of gas formation can be calculated by
considering the change in the volume of gas -
Some reactions form products that change colour
and the strength or intensity of the colour
can be measured with a spectrophotometer - Other
reactions form precipitates that can be measured

Since there are various factors that influence
the reaction rate, when investigating one factor,
the rest must be kept constant!
NOTE