1. Definitions of reaction rate(1) Average ratesDefinition 1: r = △C/△t > 0, unit: molL-l.s-lFor example:N2 + 3 H, = 2NH03.01.0t = 0 (mol·L-l)0.40.82.4t =2s (molL-1)rn2 = - (0.8-1.0)/2 = 0.1(mol·L-1.s-1)rr2 = - (2.4-3.0)/2 = 0.3 (mol·L-1.s-l)rnH3 = 0.4/2 =0.2 (mol·L-1.s-l)That is, rn2 : IH2 : InH3=1: 3: 2rn2/1 = rg2/3 = rnH3/2
6 1. Definitions of reaction rate （1）Average rates Definition 1: r = ∆C/∆t > 0, unit：mol·L-1·s-1 For example: N2 + 3 H2 = 2NH3 t = 0 (mol·L-1 ) 1.0 3.0 0 t =2s (mol·L-1 ) 0.8 2.4 0.4 rN2 = - (0.8-1.0)/2 = 0.1(mol·L-1·s-1 ) rH2 = - (2.4-3.0)/2 = 0.3 (mol·L-1·s-1 ) rNH3 = 0.4/2 =0.2 (mol·L-1·s-1 ) That is , rN2 ： rH2 ：rNH3 = 1：3：2 rN2 /1 = rH2 /3 = rNH3 /2
Def.2r = △C/(V;△t)For a reactionaA+bB→gG+hH[A]1 △[B]1△[G]1 A[H]1 ratebh△t△t△t△tagVVGVVBHAbhag
7 For a reaction a A + b B → g G + h H a b g h t H t h G t g B t b A a rate A B G H = = = = = = = − = − 1 [ ] 1 [ ] 1 [ ] 1 [ ] Def.2 r = ∆C/(Vi ∆t)
(2)Instantaneousrates（瞬时速率）r = lim △C/ △tr = lim △C/ (v;△t)△t>0△t->02N,0,= 2N,04 +0c(N205)/(mol-L-10.20022.40.20Eoaooanon0.15016.80.10A0.100I1.20,120024003600480060000(t/s)0.0505.6c(N2O5)-t关系图N,O,0.000010002000300040005000600070008000)9000瞬时速率是浓度随时间的变化率Time (s)
8 (2) Instantaneous rates (瞬时速率) r = lim ∆C/ ∆t r = lim ∆C/ (Vi ∆t) ∆t→0 ∆t→0 2N2O5 = 2N2O4 +O2 瞬时速率是浓度随时间的变化率
Example7-1 At 40.00 C in carbon tetrachloride, dinitrogenpentoxide is decomposed to oxygen according to the followingequation: 2N,O,= 2N,O +O,. According to the data used to plotFigure 7-1A, 1.15mL of STP oxygen gas were formed in the first300s 7.42 m L of STP oxygen gas were formed in the first 3000s.(1) What is the average rate of formation of STP oxygen gasduring the first 3oos? What is the average rate of formation ofSTP oxygen gas during the first 3000s? (2)What is the initial rateofformationofSTPoxygen?(2200s.9.4mL)10.00(5.000.00Figure7-1A10000200030004000Time (s)
9 Example7-1 At 40.00 C in carbon tetrachloride, dinitrogen pentoxide is decomposed to oxygen according to the following equation: 2N2O5 = 2N2O4 +O2 . According to the data used to plot Figure 7-1A, 1.15mL of STP oxygen gas were formed in the first 300s, 7.42 m L of STP oxygen gas were formed in the first 3000s. (1) What is the average rate of formation of STP oxygen gas during the first 300s? What is the average rate of formation of STP oxygen gas during the first 3000s? (2)What is the initial rate of formation of STP oxygen? Figure 7-1A
Example7-1 At 40.00 C in carbon tetrachloride, dinitrogenpentoxide is decomposed to oxygen according to the followingequation: 2N,O,= 2N,O +O,. According to the data used to plotFigure 7-1A, 1.15mL of STP oxygen gas were formed in the first300s, 7.42 mL of STP oxygen gas were formed in the first 3000s.(1) What is the average rate of formation of STP oxygen gasduring the first 3oos? What is the average rate of formation ofSTP oxygen gas during the first 3000s? (2)What is the initial rateofformationof STPoxygen?SOLUTION(1)Average rate of formation of oxygen = 1.15mL/300s= 0.00383mL/s =3.83x10-3 mL/sAverage rate of formation of oxygen =7.42/3000 =2.47 ×10-3 (mL/s)(2) slope of the tangent = (9.4-0.0) /(2200-0)= 4.3 ×10-3 (mL/s)
10 Example7-1 At 40.00 C in carbon tetrachloride, dinitrogen pentoxide is decomposed to oxygen according to the following equation: 2N2O5 = 2N2O4 +O2 . According to the data used to plot Figure 7-1A, 1.15mL of STP oxygen gas were formed in the first 300s, 7.42 mL of STP oxygen gas were formed in the first 3000s. (1) What is the average rate of formation of STP oxygen gas during the first 300s? What is the average rate of formation of STP oxygen gas during the first 3000s? (2)What is the initial rate of formation of STP oxygen? SOLUTION (1)Average rate of formation of oxygen = 1.15mL/300s = 0.00383mL/s =3.8310-3 mL/s Average rate of formation of oxygen =7.42/3000 =2.47 10-3 (mL/s) (2) slope of the tangent = (9.4-0.0) /(2200-0) = 4.3 10-3 (mL/s)