ch14---rate-equations-and-order-of-reactions.ppt

5/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 21Chapter 14Rates Equations and Order of Reactions14.1 Rates Equations and Order of Reactions14.2 Zeroth,First and Second Order Reactions14.3 Determination of Simple Rate Equations from Initial Rate Method5/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 2214.4 Determination of Simple Rate Equations from Differential Rate Equations14.5 Determination of Simple Rate Equations from Integrated Rate Equations14.6 Carbon-14 Dating5/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 23 Consider a reaction:aA+bB CRate of reaction=kAxBy(a rate law)1.x and y can only be determined experimentally and bear NO direct relationships with a and b(stoichiometric ratios)2.x=order of reaction with respect to reactant A y=order of reaction with respect to reactant B x+y=overall order of reactionk is called the rate constantNote:unit of k depends on x and yUnit:mol dm-3 s-114.1 Rates Equations and Order of Reactions(SB p.25)Rate Equations5/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 24Zeroth Order Reactions14.2 Zeroth,First and Second Order Reactions(SB p.26)A product Rate=kA =k5/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 25Example of Zeroth Order ReactionAt high pressure,gold surface saturated with adsorbed HI(g)14.2 Zeroth,First and Second Order Reactions(SB p.27)2HI(g)H2(g)+I2(g)gold surfaceRate=kHI(g)n (where n=0)Rate=kHence,the rate is independent of the concentration of HI(g)and is a constant.5/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 26First Order Reactions14.2 Zeroth,First and Second Order Reactions(SB p.27)A product Rate=k A5/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 27Examples of First Order Reaction14.2 Zeroth,First and Second Order Reactions(SB p.27)2H2O2(aq)2H2O(l)+O2(g)Rate=kH2ORate=kN2O5(g)Rate=k SO2Cl2(l)Rate=k(CH3)3CCl(l)2N2O5(g)4NO2(g)+O2(g)SO2Cl2(l)SO2(g)+Cl2(g)(CH3)3CCl(l)+OH-(aq)(CH3)3COH(l)+Cl-(aq)Rate equationReaction5/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 28Second Order Reactions(Case 1)Example:14.2 Zeroth,First and Second Order Reactions(SB p.28)2NOCl(g)2NO(g)+Cl2 Rate=kNOCl2 A products Rate=kA25/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 29Second Order Reactions(Case 2)Examples14.2 Zeroth,First and Second Order Reactions(SB p.28)A+B products Rate=kABH2(g)+I2(g)2HI(g)Rate=kH2(g)I2(g)ReactionRate equation2NO2(g)2NO(g)+O2(g)CH3Br(l)+OH-(aq)CH3OH(l)+Br-(aq)CH3COOC2H5(l)+OH-(aq)CH3COO-(aq)+C2H5OH(l)Rate=kNO2(g)2Rate=kCH3Br(l)OH-(aq)Rate=kCH3COOC2H5(l)OH-(aq)5/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 21014.3 Determination of Simple Rate Equations from Initial Rate Method (SB p.29)By determining the initial rates of reactions with different initial concentrations of reactants experimentally:For a reaction between two substances A and B,experiments with different initial concentrations of A and B were carried out.The results were as follows:Experiment Initial concentration of A(mol dm-3)Initial concentration of B(mol dm-3)Initial rate(mol dm-3 s-1)123 0.010.020.010.020.020.040.00050.00100.00205/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 21114.3 Determination of Simple Rate Equations from Initial Rate Method (SB p.29)(a)What is the order of reaction with respect to A and with respect to B?Let m be the order of reaction with respect to A,and n be the order of reaction with respect to B.Then,the rate equation for the reaction can be expressed as:Rate=kAmBnTherefore,0.0005=k(0.01)m(0.02)n(1)0.0010=k(0.02)m(0.02)n(2)0.0020=k(0.01)m(0.04)n.(3)Dividing(1)by(2),0.0005/0.0020=(0.01/0.02)m m=1 Dividing(1)by(3),0.0005/0.0020=(0.02/0.04)nn=2Answer5/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 21214.3 Determination of Simple Rate Equations from Initial Rate Method (SB p.29)(b)Calculate the rate constant using the result of experimental 1.Using the result of experiment(1),Rate=kAB20.0005=k x 0.01 x 0.022 k=125 mol-2dm6s-1(c)What is the rate equation for the reaction?Rate=125AB2AnswerAnswer5/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 213ConsideraA+bB productsBy keeping B in large excess,we have rate=kAni.e.log(rate)=nlogA+logk14.4 Determination of Simple Rate Equations from Differential Rate Equations (SB p.32)Reactions Involving More Two Reactants5/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 214Zeroth Order Reaction14.5 Determination of Simple Rate Equations from Integrated Rate Equations (SB p.37)A=-k0t+A0A product Rate=k05/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 215First Order ReactionIntegrating the above equation gives14.5 Determination of Simple Rate Equations from Integrated Rate Equations (SB p.37)In A=-k1t+InA0A product Rate=k1A5/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 216Half-life for First Order ReactionsRearranging,we haveThe time taken for half of the reactant to be converted to the product is known as the half-life of the reaction(t)14.5 Determination of Simple Rate Equations from Integrated Rate Equations (SB p.38)In A=-k1t+InA0In()=k1t t1/2=In 2/k1=0.693/k1In()=k1tIn 2=5/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 217Remark:All radioactivity decays are 1st order reaction and thus have constant half-lives.14.5 Determination of Simple Rate Equations from Integrated Rate Equations (SB p.38)Half-life of a first order reaction5/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 218Integrating the above equation givesHalf-life for Second Order Reactions14.5 Determination of Simple Rate Equations from Integrated Rate Equations (SB p.40)A product Rate=k2A25/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 219In the upper atmosphereAs long as an organism is alive,the ration of carbon-14 to carbon-12 remains constant.When the organism dies and incorporation of carbon ceases,the ratio of carbon-14 to carbon-12 decreases.Thus the age of fossil can be deduced by comparing the carbon-14 to carbon-12 with that in living tissue.14.6 Carbon-14 Dating(SB p.44)Carbon-14 Dating+5/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 220