Reaction Rates

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Reaction Rates Chemical Kinetics of the Iodine
Clock Reaction.
2
Over view

• NaHSO3 KIO3 3HSO4- I-
• We will change the concentration of the reactant
  and see how it affects the rate of the reaction.
• Determination of the Rate of a Reaction.
• Find the Order of a Reaction.
• Writing Rate Law for todays reaction
• We will change the reaction temperature and see
  how it affects the reaction rate.

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Introduction

• To understand a chemical reaction, wen need to
  know
• What happens?
• How fast does it happen?
• To what extend does it happen?
• O2 2H2 2H2O

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Chemical Kinetics

• Does the reaction want to go? This is the subject
  of chemical thermodynamics.
• If the reaction wants to go, how fast will it go?
  This is the subject of chemical kinetics.
• The study of Reaction Rates is called Chemical
  kinetics.

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Rate of a Reaction

• Reaction Rates
• The change in reactant and product concentrations
  as a function of time.
• Rate Change in concentration / Time Change
• Unit Moles / second
• Reaction rate is 1 / reaction time.

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Rate Law

• Rate law
• Rate law is an equation that gives the rate of a
  reaction as a function of the concentration of
  reactants.
• A B C D
• rate k A xby
• k rate constant
• x y represents the order of reaction

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Rate of a Reaction

• Rate can be measured two ways

How fast the Products appear
How fast the Reactant disappear
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Factors Affecting Reaction Rate
Concentration
Temperature
Surface Area
Inhibitor Catalyst
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Factors Affecting Reaction RateConcentration

• Increased concentration increases reaction rate
• more particles per volume
• more collisions

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Factors Affecting Reaction RateTemperature

• Increased temperature increases reaction rate
• molecules move faster
• making more collisions
• making higher energy collisions

11
Factors Affecting Reaction RateSurface Area

• Increased surface area increases reaction rate
• smaller particles
• collisions take place on the surface
• more area means more collisions

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Factors Affecting Reaction RateCatalyst

• A substance that speeds up a reaction without
  being used up itself.
• How does it work?
• Lowers the activation energy
• Enzymes
• Homogeneous (Same Phase as reactants)
• Heterogeneous (Different Phase as reactants)

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Factors Affecting Reaction RateInhibitor

• A substance that slows down a reaction
• It wont stop a reaction completely
• Examples
• preservatives in food and medicines

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Procedure Part I

• Influence of Concentration
• Measure 20 mL of KIO3 into a clean 125 mL and add
  30 mL of distilled water.
• Take 10 mL of NaHSO3 in a another 125 mL conical
  flask.
• Quickly mix both the solutions.
• Swirl the flask so that both the reactant mix
  well.

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Procedure Part I

• Watch the time carefully once you mix the
  solution.
• Note the exact time when a blue color appears in
  your flask.
• Do the same reaction with different amount of
  reactants.

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Calculation
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Calculation

• To find order in HSO4-
• Rate(1) kNaHSO4(1)xKIO3y
• Rate(2) kNaHSO4(2)xKIO3y
• We know the reaction rates and we know the
  concentration of NaHSO4.
• Take log on both side and then find the value of
  x.

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Calculation

• To find order in KIO3, use trial 2 and 3
• Rate(2) kNaHSO4xKIO3(2)y
• Rate(3) kNaHSO4xKIO3(3)y
• We know the reaction rates and we know the
  concentration of KIO3.
• Take log on both side and then find the value of
  y.

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Procedure Part II

• Influence of Temperature
• Measure 20 mL of KIO3 into a clean 125 mL.
• Add 30 mL of distilled water.
• Take 10 mL of NaHSO3 in a another 125 mL conical
  flask.
• Mix both the solution at room temperature and
  note the reaction rate

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Procedure Part II

• Do the same reaction with same amount the
  reactants at 0 ?C and record the reaction rate.
• Do the same reaction at 50 ?C and
• Record the reaction time and find the reaction
  rate.
• Find out what is the influence of temperature

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Part II
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Notes

• Work in Pairs.
• You will sudden change in color (from colorless
  to blue), so dont scare or dont drop the
  glassware!
• You have to bring both the reactant to the
  mentioned temperature before mixing.
• Volumes are pre-set for NaHSO3 and KIO3.
• Dont forget to add one or two drops of starch as
  indicator.