14.1 Chemical Kinetics
   
     Study of how rapidly a reaction will occur. In 
     addition to speed of reaction, kinetics also 
     deals with the reaction mechanism (exactly 
     how the reaction occurs)
   1. Factors that affect reaction rate
     1. Concentration of reactants – more particles means 
        more frequent “effective” collisions occur
     2. Temperature – higher temps, the molecules have 
        more KE, are moving faster and are more likely to 
        collide
     3. Catalyst – chemical that speeds up a reaction by 
        changing the reaction mechanism, not consumed in 
        reaction
     4. Physical state of reactants – (phase)
     5. Surface area (for solids) – greater SA = faster 
        reaction
               14.2 Reaction Rate
   
    The change in concentration of reactants or 
    products over time. 
     The rate can be expressed as a rate of decomposition 
      of reactants or rate of production of products.
   
   
     What is the average rate of decomposition of “A” 
      
             st                                    nd
     in the 1  20 seconds of the reaction? In the 2  20 
     seconds?
   
     Rate =-   = -    =  0.023 mol/sec
   
     Rate =-   = 0.012 mol/sec
   
     What is the average rate of appearance of 
                  st
     “B” in the 1  20 seconds of the reaction? In 
          nd
     the 2  2o seconds?
   
     Rate= =   = 0.023 mol/sec
   
     Rate =   = -0.012 mol/sec
   
     Chemical Equation showing mol ratio of A 
     changing into B:  1A → 1B
                Mathematical Expressions for 
                                         Reactions
     
        Reaction:  N                    +  3 H              →  2NH
                                 2(g)                2(g)               3(g)
     ***If you want to compare the rates using 
     different substances, you use the mole ratios
     
        The rate of reaction is always positive, and is 
        usually measured in M/s
         Under certain conditions, the rate of formation of NH  
                                                                                                  3
           is 0.28 M/s. What is the rate of change for N ?
                                                                                   2
         0.28 M NH           1 mol N            = 0.14 M/s                 
                             3                       2
                                                          s         2 mol NH
                                                                                    3
    
    
       Indicate how the rate of disappearance of each reactant is 
        
       related to the rate of appearance of each product:
    1.     H O     → H  + O
            2  2(g)     2(g)    2(g)
         -=  = 
    2.   2SO      +  O     → 2SO
              2(g)     2(g)        3(g)
            (-   =  -   =    )2
                - ∆[SO ]/∆t  =  -2∆[O ]/ ∆t  = ∆[SO ]/∆t 
                      2                 2               3
         *SO will disappear and SO will appear at twice the rate of 
             2                            3 
         O
           2