Chem 1465 1st Edition Lecture 20Outline of Last Lecture 1. Possible test questionsOutline of Current Lecture1. Rate of chemical reactionsA. DefinitionB. Stoichiometry C. Average rate vs instantaneous rates2. Rate laws and concentrationsA. DefinitionB. Order of reactionCurrent Lecture1. Rate of chemical reactionsA. Definition: change that occurs in a given time; change in concentration per unit in time. - For the reaction: A → B Rate = Δ[B] / Δt Rate = -Δ[A] / Δt B. Stoichiometry- For the reaction: 2A3 → 3A2 we cannot simply plug into the rate equations shown above. We must normalize. Rate = 13(Δ[A 2]Δt) Rate = −12(Δ[A 3]Δt) C. Average rate vs instantaneous rate- Average rate is the rate calculated by 2 concentrations measured a different times- Instantaneous rate is the rate measured at a particular point in time These 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.- When thinking about kinetic we prefer to use instantaneous rates, especially using time equal to zero 2. Rate laws and concentrationsA. Definition: expressing the rate in the concentrations (aA +bB → products)- Rate = k [A]n [B]mWhere k is the rate constant, A and B are concentrations, m and n are values that must be experimentally determined. Reaction order corresponds to m and n where m is the order of B and n is the order of A. B. Order of reaction: tells us the units of k Zeroth order Rate = k M s-1First order Rate = k [A] s-1Second order Rate = k [A][B] orRate = k [A]2 M-1s-1Third order Rate = k [A][B]2 or Rate = k
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