3.2 Brief introduction of effect of concentration of reactants on reaction rate -the rate expression -3.2.1 The rate expression
§3.2 Brief introduction of effect of concentration of reactants on reaction rate —the rate expression 3.2.1 The rate expression
3.2.1 The rate expression The ratio of the decomposition reaction rate of N2Os to the concentration of N2Os in CCla at 40C 2N20s(CC4)-→2N204(CCl4)+O2(g) t/s v:cNOs)/s t/s v:dNO)/s- 0 3.65×10-4 1800 3.64×104 300 3.59×104 2400 3.62×104 600 3.60×10-4 3000 3.69×104 900 3.62×10-4 4200 3.61×104 1200 3.61×10-4 5400 3.68×104 The ratio is constant.Therefore,the reaction rate v is directly proportional to c(N2O): v=kc(N2Os)
The ratio of the decomposition reaction rate of N 2 O5 to the concentration of N 2 O5 in CCl4 at 40 ℃ t /s t /s 0 1800 300 2400 600 3000 900 4200 1200 5400 ( ) 1 5 s/ON: 2 − υ c 4 1065.3 − × 4 1060.3 − × 4 1062.3 − × 4 1061.3 − × 4 1059.3 − × 4 1069.3 − × 4 1062.3 − × 4 1064.3 − × 4 1068.3 − × 4 1061.3 − × ( ) 1 5 s/ON: 2 − υ c 3.2.1 The rate expression The ratio is constant. Therefore, the reaction rate υ is directly proportional to c(N 2 O 5): )ON( 52 υ = kc 2N 2 O 5(CCl 4 ) → 2N 2 O 4(CCl 4)+ O 2(g)
For the general reaction: aA+bB→yY+zZ v=kckc a,B-the order of a reaction for a particular reactant:If a =1,the reaction is first order in A; B=2,the reaction is second order in B.a+B=3,the overall reaction order is three.The value of a,B must be determined by experiment.Generally speaking, a≠a,B≠b. k-rate constant:zero order reactions,mol-L-1's1; first order reactions,s1;second order reactions,(mol L 1)1s;Any change in concentration has no effect on the rate constant.However,temperature can affect the value of k
For the general reaction ： α,β—the order of a reaction for a particular reactant：If α = 1 ，the reaction is first order in A; β =2, the reaction is second order in B. α + β = 3 ，the overall reaction order is three. The value of α，β must be determined by experiment. Generally speaking, α≠a,β≠b. k —rate constant：zero order reactions, mol·L-1 ·s-1； first order reactions, s-1；second order reactions, (mol·L -1 )-1 ·s-1； Any change in concentration has no effect on the rate constant. However, temperature can affect the value of k. + ba → y + zZYBA βα υ BA = ckc