Order of reaction 
     It is the no of atoms or molecules whose concentration determine the rate of 
        reaction.
     n A+n B+n C                     products
       1   2   3
     Rate = 
     Order = n  + n  + n  
              1   2   3
     Reactions may be also classified according to molecularity.
     Factors affecting rate of reaction 
     •  Temperature.
     •  Catalysts.
     •  Conc. .
     Half-time : the period of time required for a drug to decompose to one half the 
        original concentration .
     Shelf time : time required for a drug to loss 10% of its original concentration .   
      
  Experimental work 
  Determination of specific reaction rate ethyl 
   acetate in presence of 1N HCL
  Procedures:
  1. In a dry clean stopped conical flask put 18 C.C. dist H2O 
    and 20 ml 1 N HCL.
  2. To this mixture, add 2 C.C. ethyl acetate.
  3. In another flask (titration flask) put 30 C.C. dist. H2O (by a 
    measure) and transfer 5 ml of the mixture into the 
    titration flask (use pepett) (water is added to decrease the 
    effect of ethyl acetate).
  4. Titrate against 4N NaOH using Ph.Ph. indicator at 0 time or 
    blank E.P. = HCL.
  5. i.e. E.P.o = b = HCL 
  6. Repeat the titiation after different time intervals: 
    5,15,30,40,50. 
        Calculation:
          CH COOEt + H O  CH COOH + EtOH
             3           2      3
         
        This is first order bimolecular reaction.
        At 0 time:  CH3COOEt is not affected.
        So  E.P. = HCL (blank, b.)
        After 5: 
        E.P. = HCL + CH COOH (formed by hydrolysis or degradation)
                        3
        E.P. after 5 – b. = HAc
          = ml of NaOH equivalent to Hac
        = ml of NaOH equivalent to decomposed ethyl acetate after 5 min.
        (N * V- b)     = (N * V)     (= no. of mols of Ac presence in the sample)
                  NaOH          EtAc 
        1n NaOH = 1n HAC = 1n Et Ac   ( V        = 5 ml)
                                             EtAc
        N = M 
        W   =  no. of mols * 88 (gm/mol Et Ac) 
           2 
        W 1(first used)  = d * V (2 ml) Et Ac
        W remaining in solution = W1 – W2 
        % Percentage remaining = [(W  – W ) / (W  + W )] * 100
                                         1    2       1     2 
        And so a calculation is performed at other time intervals 
        The results are written in a table:
        Log % remaining       Percentage              E.P                 Time
                               remaining
                                                                           0
                                                                           5
                                                                          15
                                                                          30
                                                                          40
                                                                          50