IB Topic 6: Kinetics 6'1: Rates of Reaction

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IB Topic 6 Kinetics6.1 Rates of Reaction

• 6.1.1 Define the term rate of reaction
• 6.1.2 Describe suitable experimental procedures
  for measuring rates of reactions
• 6.1.3 Analyse data from rate experiments

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6.1.1 Define the term rate of reaction

• Rate of Reaction
• Some reactions occur rapidly
• Inflation of an airbag (pg. 111 IBCC)
• Explosion of nitrogen triiodide
• Some reactions occur slowly
• Reaction of pigments in paintings with light
  pollutants
• (pg. 111-112 IBCC)
• Tarnishing of silver/Iron rusting

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6.1.1 Define the term rate of reaction

• Rate of Reaction
• An increase in concentration of one of the
  products per unit time or as the decrease in
  concentration of one of the reactants per unit
  time.
• Units of rate of reaction
• moles per dm3 per second (mol dm-3 s-1)

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6.1.2 Describe suitable experimental procedures
for measuring rates of reactions

• Measuring the Rate of Reaction
• Mass or volume changes for gaseous reactions
• Change in pH for reactions involving acids or
  bases
• Change in conductivity measurements for reactions
  involving electrolytes
• Use of a spectrophotometer or colorimeter for
  reactions involving color changes

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6.1.2 Describe suitable experimental procedures
for measuring rates of reactions

• Measuring the Rate of Reaction

• Measuring the Rate of Reaction

• The graph shows the volume of CO2 produced
  against time when excess CaCO3 is added to HCl

• The graph shows the concentration of a reactant
  against time

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6.1.3 Analyse data from rate experiments

• Consider the hypothetical aqueous reaction
• A(aq) ? B(aq)
• A 100.0 mL flask initially contains 0.065 mol of
  A and
• 0 mol B. The following data are collected
• a) Calculate the number of moles of B at each
  time in the table.
• b) Graph the change in amount of A B over time.
• c) Calculate the average rate of disappearance of
  A for each 10-minute interval in terms of mol s-1
• d) Between t10 min t30 min, what is the
  average rate of appearance of B in units of mol
  dm-3 s-1

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6.1.3 Analyse data from rate experiments

• a) Calculate the number of moles of B at each
  time in the table.

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6.1.3 Analyse data from rate experiments
b) Graph the change in amount of A B over time.
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6.1.3 Analyse data from rate experiments.042-.051

• c) Calculate the average rate of disappearance of
  A for each 10-minute interval in terms of mol s-1
• 0 min?10 min (.051-.065)/600 2.3 x 10-5 mol
  s-1
• 10 min?20 min (.042-.051)/600 1.5 x 10-5 mol
  s-1
• 20 min?30 min (.036-.042)/600 1.0 x 10-5 mol
  s-1
• 30 min?40 min (.031-.036)/600 0.8 x 10-5 mol
  s-1

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6.1.3 Analyse data from rate experiments

• d) Between t10 min t30 min, what is the
  average rate of appearance of B in units of M s-1
• B at 10 min 0.014 mol/.100 dm3 .14 M
• B at 30 min 0.029 mol/.100 dm3 .29 M
• Rate (.29-.14)/1200 1.3 x 10-4 mol dm-3 s-1

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IB Topic 6 Kinetics6.2 Collision Theory

• 6.2.1 Describe the kinetic theory in terms of the
  movement of particles whose average energy is
  proportional to temperature in Kelvins.
• 6.2.2 Define the term activation energy, Ea.
• 6.2.3 Describe the collision theory.
• 6.2.4 Predict and explain, using the collision
  theory, the qualitative effects of particle size,
  temperature, concentration and pressure on the
  rate of a reaction.
• 6.2.5 Sketch and explain qualitatively the
  Maxwell-Boltzman energy distribution curve for a
  fixed amount of gas at different temperatures and
  its consequences for changes in reaction rate.
• 6.2.6 Describe the effect of a catalyst on a
  chemical reaction.
• 6.2.7 Sketch and explain Maxwell-Boltzmann curves
  for reactions with and without catalysts.

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6.2.1 Describe the kinetic theory in terms of the
movement of particles whose average energy is
proportional to temperature in Kelvins.

• Kinetic Theory
• Tiny particles in all forms of matter are in
  constant motion.
• The energy an object has because of motion is
  called kinetic energy.
• The particles in any collection of atoms or
  molecules at a given temperature have a wide
  range of kinetic energies, from very low to very
  high. Overall, there is an average kinetic
  energy.

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6.2.1 Describe the kinetic theory in terms of the
movement of particles whose average energy is
proportional to temperature in Kelvins.

• What happens when a substance is heated?
• Particles absorb energy, some of which is stored
  within the particles (potential energy). This
  does not affect temperature.
• The remaining energy speeds up particles
  (increases the average kinetic energy) which
  increases temperature.

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6.2.1 Describe the kinetic theory in terms of the
movement of particles whose average energy is
proportional to temperature in Kelvins.

• Kelvin Temperature
• As a substance cools, the average kinetic energy
  declines and the particles move more slowly.
• At some point, the temperature will be low enough
  so the particles will stop moving and have no
  kinetic energy. That point is called absolute
  zero (0 K , -273.15 oC)
• Kelvin temperature of a substance is directly
  proportional to the average kinetic energy of the
  particles. The particles in helium gas at 200 K
  have twice the average as the particles in helium
  gas at 100K

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6.2.2 Define the term activation energy, Ea.

• Activation energy is the minimum amount of
  kinetic energy that must be given to the
  reactants before they will react.
• (a) Activation energy (Ea) of forward reaction
• (b) Activation energy (Ea) of reverse reaction
• (c) Heat of reaction (?H)
• 1) What is the heat of reaction for each of the
  graphs? Which is exothermic and which is
  endothermic?

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6.2.3 Describe the collision theory.

• The two particles (atoms, ions, radicals or
  molecules) must collide with each other.
• They must collide in the correct orientation, so
  that the reactive parts of each of the two
  particles come into contact with each other.
• They must collide with sufficient kinetic energy
  to bring about the reaction.

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6.2.4 Predict and explain, using the collision
theory, the qualitative effects of particle size,
temperature, concentration and pressure on the
rate of a reaction.

• Decreasing the particle size of solid reactants
  increases the reaction rate.
• Increasing the temperature increases the reaction
  rate.

• Only the surface particles of a solid react.
  Breaking the solid into smaller pieces increases
  the surface area so more particles available to
  react.
• At higher temperatures the particles move faster
  and have more energy. Faster movement means more
  collisions, more energy means more collisions
  have the activation energy required for reacting.

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6.2.4 Predict and explain, using the collision
theory, the qualitative effects of particle size,
temperature, concentration and pressure on the
rate of a reaction.

• Increasing the concentration of the reactants
  increase the reaction rate
• Increasing the pressure of a gaseous reaction
  increases the reaction rate.

• More particles present means more collisions.
• Increasing pressure translates to increased
  concentration by either reducing the volume or
  increasing the number of particles. Higher
  concentration means more collisions.

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6.2.5 Sketch and explain qualitatively the
Maxwell-Boltzman energy distribution curve for a
fixed amount of gas at different temperatures and
its consequences for changes in reaction rate.

• Area under the graph directly related to the
  number of particles present. The average kinetic
  energy close to the peak of the graph. Area to
  the right of the Ea depicts the number of
  particles having sufficient energy to react.
• At higher temps, the distribution flattens out as
  more molecules gain kinetic energy. Area under
  the curves remain the same since the number of
  particles remain the same. However more particles
  have kinetic energies greater than the Ea as
  temperature increases.

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6.2.6 Describe the effect of a catalyst on a
chemical reaction.

• A catalyst is a substance that increases the rate
  of a chemical reaction without itself being
  chemically changed at the end of the reaction.
• Catalysts lower the activation energy barrier by
  positioning reactant particles favorably. More
  reactant particles possess this lower activation
  energy so the rate increases.

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6.2.7 Sketch and explain Maxwell-Boltzmann curves
for reactions with and without catalysts.

• A catalyst is a substance that increases the rate
  of a chemical reaction without itself being
  chemically changed at the end of the reaction.
• Catalysts lower the activation energy barrier by
  positioning reactant particles favorably. More
  reactant particles possess this lower activation
  energy so the rate increases.

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