kinetics - 13-1 KINETICSThe rate at which chemical...

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Unformatted text preview: 13-1 KINETICSThe rate at which chemical reactions proceed is defined mathematically as: What influences the rate of a reaction? The rate of a reaction can change over time. The initial rate of the reaction will most likely be different than the rate after a specific amount of time. The speed of a reaction is measured by the change in concentration with time. For a reaction A →B Instantaneous rate – Average rate – 13-2 Example: Write the rate for each of the following reactions in terms of each product and reactant and draw a graph representing the relative change in concentrations over time. 2 A + B →2 C A + 3 B + 5 C →4 D + 2 E How do you write the overall rate equation for the reaction? What does the overall rate equation tell us? For any reaction that is reversible, there is a forward and reverse rate.The Δ[A] depends upon both the forward reaction rate and the reverse reaction rate. This can complicate the evaluation of the overall reaction rate. To find the reaction rate, which will allows us to calculate the reaction rate constant (k) and the reaction order, we must pick conditions such that the forward rate of reaction is much greater than the reverse reaction rate. When would this occur?13-3 There are two main things as chemists and scientists that we want to investigate with respect to reaction kinetics. 1.What is the reaction rate dependence on concentration? 2.What is the concentration of a product or reactant at a specific point in time of the reaction? Differential Rate Law(reaction rate as a function of concentration)A BRate = Where:n = k = Both nand kmust be determined experimentally (nis often the same as the stoichiometric coefficient in the balanced chemical equation; However, this is not always true!) 13-4 Method of Initial RatesDetermination of the Differential Rate Law by finding the rate constant (k), the reaction order, and the rate law of a reaction. 1)Find the slope of the curve (conc. vs. time) near the beginning of the reaction. 2)Change the reactant concentrations and find the initial rate again. 3)Repeat part 2 until there is at least 1 more experiment than the number of reactants 4)Use this information to mathematically determine the rate law of the reaction. 13-5 Example: Use the following information to determine the order of each reactant, the overall reaction order, and the rate constant. (You are essentially trying to find the rate law for this reaction) 2 A + B →C + D initial rate of Exp.# initial [A] initial [B] formation of C (M/s) 1 0.30 0.30 0.522 0.30 0.60 1.053 0.60 0.60 4.2013-6 Example: Nitric oxide reacts with hydrogen to give nitrogen and water. In a series of experiments the following initial rates were obtained. Find the rate law and the value for the rate constant (k)....
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kinetics - 13-1 KINETICSThe rate at which chemical...

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