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kineticssummary08 - AP Chemistry Kinetics Notes Plotting...

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AP Chemistry Kinetics Notes Plotting the concentration of a chemical in a reaction as a function of time is called a Kinetic Curve or Concentration vs. Time Curve Calculate the slope at a given time by drawing a tangent at that point and calculating the slope of the line. This is the derivative of the function at that point Always use a positive value for rate Rate = Δ C products / Δ t Rate = - Δ C reactants / Δ t Once the rate of one component is determined, others can be determined using stoichiometric ratios. Units: mol/Ls or mol L -1 s -1 Reaction Rate Factors 1. Concentration of reactants 2. Temperature (Increasing temperature increases the reaction rates) 3. Catalyst (Substance that participates but is not changed by the reaction. It is not included in the balanced equation The general rate of reaction is obtained by dividing the rate of disappearance of a reactant or the rate of formation of a product by the stoichiometric coefficient of that reactant or product in the balanced chemical equation. For equation aA + bB cC + dD The general rate of reaction is: Rate = -(1/a) Δ [A]/ Δ t = -(1/b) Δ [B]/ Δ t = (1/c) Δ [C]/ Δ t = (1/d) Δ [D]/ Δ t This represents the average rate of a reaction over a time interval, as the rate is generally greater when the concentration of reactant(s) is greater. Details 1. Concentration Expressed in the rate law Rate = k[A] x [B] y [C] z k = rate constant -Exponents are usually small whole numbers but may be negative or rational fractions -They are NOT stoichiometric coefficients. -The rate law must be determined experimentally. There is no theoretical way to predict exponents. The rate law is determined by taking the ratios of experimental results on a reaction such that one or more of the concentrations cancel out leaving one to be determined Ex: Rate 2 = k[.1] x [.2] y Rate 1 k[.05] x [.2] y This is sort of a process of elimination
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After the exponents are determined, k may be determined from any of the reactions (see section in text for examples) Order of the rate law Either: 1. refers to the individual exponents of each component Or 2. refers to the sum of all of them for the overall reaction The units of the rate constant k vary with the order of the rate law, however they must be such that the overall rate is given in units of concentration per unit time. If the concentration of a component has no effect on the reaction rate (i.e. zeroth order) it is not included
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kineticssummary08 - AP Chemistry Kinetics Notes Plotting...

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