Chem 113 1st Edition Lecture 11Outline of Last Lecture I. Determining Reaction Order and Rate ConstantII. Kinetics: Rate LawsIII. Reaction half-lifeOutline of Current LectureI. Half-life relationshipsII. Reaction rates, temperature, and the Arrhenius EquationIII. Activation energyIV. Molecular structure and reaction rateCurrent LectureI. Half-life relationshipsa. First order:i. Doesn’t depend on concentrationii.t1 /2=ln 2kb. Second orderi. Depends inversely on initial concentrationii.t1 /2=1k [ A ]0c. Zeroth orderi. Depends directly on initial concentrationii.t1 /2=[ A ]02 kII. Reaction rates, temperature, and the Arrhenius Equationa. The basic principle of collision theory is that particles must collide in order to reactThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.b. And increase in the concentration of a reactant leads to a larger number of collisions, hence increasing reaction ratec. The number of collisions depends on the product of the numbers of reactant particles/concentrationsi. Concentrations are multiplied in the rate law, not addedd. Temperature and the rate constanti. Temperature has a dramatic effect on reaction rateii. Experimental data shows that k increases exponentially as T increases, this is expressed in the Arrhenius equation1.k =A e−Ea/ RTa. k= rate constantb. A= frequency factorc. Ea= activation energy2. Higher T larger k increased rateIII. Activation energya. In order to be effective, collisions between particles must exceed a certain energythresholdb. When particles collide effectively, they reach an activated state. The energy difference between the reactants and the activated state is the activation energy (Ea ) for the reactionc. The lower the activation energy, the faster the reactioni. Smaller Ea larger f larger k increased rated. Calculating activation energy:i. Can be calculated from the Arrhenius equation1. Straight line form6. : lnk =lnA−EaR(1T)7. If data is available at two different temperatures: lnk2k1=−EaR(1T2−1T1)IV. Molecular structure and reaction ratea. For a collision between particles to be effective, it must have both sufficient energy and the appropriate relative orientation between the reacting particlesi. Atoms that become bonded in products must make contactb. The term A in the Arrhenius equation is the frequency factor for the reaction, has the same units as ki. A=pZ1. P= orientation probability factor2. Z= collision frequencyii. The term p is specific for each reaction and is related to the structural complexity of the reactants1. Single atoms are spherical and have p-values of about 12. More complicated values have p-values of more than oneV. Transition State Theorya. An effective collision between particles leads to the formation of a transition state or activated complexb. The transition state is an unstable species that contains partial bonds. It is a transitional species partway between reactants and productsi. Transition states cannot be isolatedc. The transition state exists at the point of maximum potential energyi. The energy required to form the transition state is the activation energyZero Order First Order Second OrderRate Law Rate=k Rate=k[A] Rate=k[A]2Units for k mol/L*s 1/s L/mol*sHalf-life[ A ]02 kln 2k1k [ A ]0Integrated Rate Law in straight-line form[ A ]t=−kt +[ A ]0ln [ A]t=−kt +ln [ A]01[ A ]t=kt +1[ A ]0Plot for straight line [A]t vs. t ln[A]t vs. t1[ A ]t vs.tSlope, y-intercept -k, [A]0-k, ln[A]0k, 1[ A
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