Kinetics I&II 

• Reaction rate = k [A]^y [B]^x

• ●  K is the rate constant which we will be given

• ●  [ ] represents concentration of A/B which represents the reactants (or potentially

  products)

• ●  ^x/y represents the order of the reactant or product in the it can be 0, 1 or 2

• ●  IF IT IS 0 the reactant does not affect the rate of the reaction

• ●  We will be given a table where we may not know the rate equation so then there will be 3

  experiments with the initial moles of the reactants being kept constant and changing with the initial rate of reaction if the initial increases by 4x te order of the ration is 2 if it is only 2 times it is 1 order of reaction

• -  Chemical equation says nothing about the rate of the reaction

• -  The change in the rate of the reaction is defined as change in the concentration of a

  product divided by the time for the change to occur

• -  The rate of the reaction is not constant, an exothermic reaction will increase and thus as

  the temperature rises the rate of reaction

• -  A concentration-time graph can thus be plotted in order, the gradient gives the rate of the

  reaction at any time

• -  Practical measures ideally do not interfere with the reaction mixture

  - Gas syringe to measure volume of gas produced from a reaction
  - Colourimetry
  - Difference in the weight of the reaction mixture
  - React, quench at different times and then titrate to gain concentration of reactant

• -  Rate equation shows the way in which the concentrations of the reactants affect the rate of a reaction

• -  Rate = k[X][Y]^z

• -  With z and any other power being the

• -  Overall reaction order is the powers added together

• -  Rate constant k is the only constant at a set temperature, if the temperature changes the

  k value will differ

• -  1st Order Reactions:

  • -  Rate of the reaction is proportional to the concentration of that reactant

  • -  Thus doubling the concentration of the chemical X leads to a doubling of the rate

    of the reaction

  • -  Rate v concentration graph will give a straight line with a positive gradient

  • -  Concentration v time graph will give constant half tives

• -  2nd order reaction:

  • -  Rate of the reaction is proportional to the concentration of that reactant squared

  • -  Thus doubling the concentration of X increases the rate by a factor of 4

  • -  Rate v concentration reaction is curved line as opposed to a straight line like for a

    first order reaction

  • -  Concentration v time graph has unequal half lives

• -  0 order reaction:

  • -  Rate is unaffected by changes to the concentration of the reactant

  • -  Rate v concentration straight line no change

  • -  Concentration v time graph does not change with time and it has a constant

    negative gradient so it is a straight line downward

• -  Initial rate method

  • -  Acts to find the rate directly after the start of the reaction and thus all of the concentrations are known

  • -  Thus multiple in which all concentrations are the same bar one which is the species for which the order of reaction will be deduced

• -  Clock reaction

  • -  Produces a colour change after a period of time where a set concentration of one

    reactant is present

  • -  A reaction will often be with iodide ions so an example would be H2O2

    - H2O2+2H++2I-→I2+2H2O

  • -  A small amount sodium thiosulfate ions are added to the reaction which at first

    react with the iodine which does not lead to a colour change as the the iodine is changed essentially back to iodide ions colour changes to blue-black immediately and the time taken for the colour change to occur can be notes

  • -  When all the thiosulphate is used up the

  • -  The amount of thiosulphate used has to be constant to assure that the rate at

    which the same volume of iodine is formed is recorded

• -  Multi-step reaction

  • -  The rate-determining step is the slowest of the reaction and has the highest activation energy

  • -  Sn1 reaction have 1 rate determining step

  • -  Sn2 reactions have 2 rate determining steps

• -  Arrhenius Equation

  • -  Raising temperature has a large effect on the rate of the reaction, especially when covalent bonds are broken

  • -  Value of rate constant (k) usually increases as the temperature increases and thus the rate of the reaction increases

  • -  The activation energy is explained as the transitions state of a reaction is at a higher energy level and as a result there is an energy barrier which is the activation energy

  • -  Natural log of the rate constant against 1/T was found to have a straight line

  • -  k = Ae^-Ea/RT

    • -  k is the reaction constant

    • -  A is the Arrhenisu constant

    • -  e is on your calculator

    • -  R is the gas constant

    • -  T is the temperature in Kelvin

    • -  Ea is the activation energy

  • -  Alternate form if taking the natural log of both sides is

- lnK = -Ea/R x 1/T + constant