Kinetics definition - defintion PDF

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Kinetics definition Average rate  The average rate is the change in rate over a time interval

Instantaneous rate  Instantaneous rate is the rate at a specific point in time during the course of the reaction

Rate law  Relationship between rate and concentration  E.g. rate ∝ [A] / rate = k[A] Reaction rate  The change in concentration of a reactant over time Rate constant  Proportionality constant (k) in rate law  E.g. for a 1st order reaction: rate =k[conc] First order reaction  Where the overall reaction order in the rate law is one reaction  Rate ∝ [A] Third order reaction  Where the overall reaction order in the rate law is three  The rate is 3rd order in as single reactant or 2nd order in one and 1st order in another or 1st order in each of three reactants  Rate ∝ [A]3 / rate ∝ [A]2[B] / rate ∝ [A][B][C]

Half life  Time taken for concentration of reactant to fall to half its initial value  E.g. for a 1st order reaction t1/2 = In2/k Activation energy  Activation energy (Ea) is the energy required by the reactants to reach the transition state Reaction profile  A graph showing the reaction pathway/reaction coordinates versus energy Boltzmann distribution  The distribution that temperature is proportional to average molecule energy Reaction mechanism  The overall sequence of steps Rate determining step  Overall reaction rate depends on the rate of the slowest step Reactive intermediate  Represent points of minimum energy on the overall reaction Transition state  The transition state in an elementary reaction is the point of highest energy between reactants and products Catalyst  Catalyst are substances that speed up a reaction without being consumed in the overall process Homogeneous catalyst (usually appear in rate law)  Catalyst that work in the same phase as the reaction Heterogeneous catalyst  A heterogeneous catalyst is in a different phase to the reactants  E.g. Pt(solid) in the hydrogenation of alkenes(gas) Arrhenius equation  Arrhenius equation gives the relationship for the temperature dependence of the reaction rate constant  k = Ae-Ea/RT Uncatalyzed  Reaction 1 has lower activation energy Rhodium catalyst

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Reaction 1 unchanged, but reaction 2 has a new low energy pathway

Reaction mechanism  A series of elementary step Rate limiting step  One of these steps determines the rate of reaction...