Rate of reaction - Form 5

 1. Rate of reaction -   the changes occur / time taken for the changes to happen.
 2. There are 2 type of ROR-
      - average ROR - the total time taken for changes measured.
      - instantaneous ROR - the changes take place at a given time
 3. To calculate the average ROR is by measure the total changes occur and divide by the total time taken
     until the reaction is stopped.
     Example: The reaction of zink with hydrochloric acid-
                    a) the volume of hydrogen gas given off = 35.0 cm3.
                    b) the total time for reaction to stopped = 210 s
     So, the Average ROR = 35.0 / 210 = 0.17 cm3/s
  4. To calculate the instantaneous ROR -
      - you a need a graph of the reactant deacreases / product increases( Y axis) against the time ( X axis).
      - use a ruler to draw a tangen close to the point on the graph at given time.
        ( if the reactant decreases graph- make sure the tangen is not over/cross the curve of your graph )
        ( if the product increases graph - make sure the tangen is on top of the curve and not crossing the curve)
       - from the tangen draw a triangle and find the lengh of Y axis for the trianle  = dY, and
         and find the lenght of X axis for the trangle = dX
       - the Instanteneaous ROR  is  dY / dX.
       - tips - make sure the graph is evently scaled and the curve is smooth.
 5. Operation definition for Rate of  Reaction ( ROR) -
       - To measure the time taken for changes to occur ( the responding variable )  by using 
          stopwatch.
       - the responding variable could be the volume of gas liberated, decreases of reactant mass, increases
          of  product mass or the increases or decreases of temperature.
 4. There are 5 factors that affect the ROR-
       a) size of reactant - the bigger the size, the smaller the expose surface area.  so, the less number
           of collision to occur. Therefor the lower frequency of collision and the lower rate of reaction.
          - the smaller the size of reactant, the larger total surface area. So, the more collision to occur.
            Therefor the higher frequency of collision, effective collision and the higher rate of reaction.
          - Example of experiment - 20g of calcium carbonate chips and 20g of calsium                          
            carbonate powder with  25 cm3 of 0.5 moldm-3 Hydrochloric acid. The total rate of  reaction is
            calculated by measure the volume of Hydogen gas released per time taken. The apparatus needed
            are burette, basin, stopper with deliver tube, conical flask, measuring cylinder ,retort stand and stop
            watch.
       b) concentration of reactant -
          - when concentration of reactant is high, the more reactant can collide and more effective 
            collision occur. Therefor the ror is high.
          - when concentration of reactant is low, the less reactant can collide. Therefor the ror is low.
          - Example of experiment - 45cm3 of 0.5 moldm-3 sodium thiosulphate with  5 cm3 of 0.5 moldm-3
             Hydrochloric acid. The total rate of  reaction is calculated by measure the time taken of marked (on
             a white paper )dissappear.the experiment is repeated with different volume of Sodium thiosulphate in
             the solution. The apparatus needed are conical flask, measuring cylinder, filter paper, white paper
             with marked and stopwatch.

       c) temperature of solution -
         - when the temperature of solution is high , the particles of reactants have more kinetic 
            energy and it moves faster. Therefor more effective collision take place. So,the ROR is high.
         - cooling a mixture will slow down theparticles of reactants. so, fewer collisions take place and ROR is
           low.
        - Example of experiment - 45cm3 of 0.5 moldm-3 sodium thiosulphate with  5 cm3 of 0.5 moldm-3
           Hydrochloric acid. The total rate of  reaction is calculated by measure the time taken of marked (on a
           white paper )dissappear.The experiment is repeated with different temperature of Sodium thiosulphate
           solution. The apparatus needed are conical flask, measuring cylinder, filter paper, white paper with
           marked,thermometer and stop watch.

      d) Pressure on reactants -
         - the higher pressure will decrease the volume of reactants. Therefor the                       
           distance between particles is small.( the reactant is closer ). So, more effective                               
           collisions will take place and the ROR is higher.                              
       e) Catalyst on reaction -
        - all reactions require energy . the reaction only occur if the reactants achieved the energy level. The
          energy needed is called Activation Energy, Ea. The reaction only can happen if the reactants achieve at
          least (or more) than Ea.
       - the presence of catalyst will lowered the energy level. Therefor the reaction                            
          takes place faster because more reactants are easier to collide and react.
      -  Example of experiment - The decomposition of Hydrogen peroxide 20 - volume. The total rate of
          reaction is calculated by measure the time taken of glowing splinter to ignite.The experiment is
          repeated with the presence of Manganese (iv)oxide as catalst. The apparatus needed are conical flask,
          measuring cylinder, glowing splinter and stop watch.
       - application of catalyst in industry and daily life:
          i ) Combustion of charcoal - smaller sizes in burning with oxygen.
         ii ) Storing food in refrigerator - cold place to keep food stay fresh longer
            - to lower the activiteis of bacteria
         iii) Cooking food in Pressure Cooker - the higher pressure will increase the cooking temperature and
              the food is cooked faster.
        iv ) Haber Process - presence of iron powder as catalyst. The magnufacture of ammonia is faster.
        v  ) Contact Process - presence of Vanadium (v) oxide as catalyst, at 500C and pressure of 2 to 3
              atmosphere.The magnufacturer of Sulphuric acid.
        vi ) Ostwald Process - Combination of Platinum and Rhodium as catalyst in 850C and pressure of 5
              amp. The magnufacturer of Nitric acid.