What was the original concentration if, after 2.00 minutes, the reactant concentration is 0.062 M? Problem #10: The half-life for a first-order reaction is 32.0 s. Solution: The 50.0% decomposed tells us that the 17.5 min is the half-life.Ĭan also be used. What is the rate constant of the reaction Problem #9: In a first-order decomposition reaction, 50.0% of a compound decomposes in 17.5 min. Note that part c involves a time frame slightly less than one half-life, so the ending concentration is slightly more than 0.05 M. (c) If you started the reaction with = 0.1 M, what would be the hydrogen peroxide concentration after 15.0 minutes? (b) If you had a bottle of H 2O 2, how long would it take for 86% to decompose? (a) What is the rate constant of the reaction? (Which is different from the problem above. The half-life of the reaction is 17.0 minutes. Problem #8: The decomposition of hydrogen peroxide is a first-order reaction. Since one half-life equals 6.5 hrs, two half-lives would take 13.0 hrs. Solution (specific to this problem): 0.70 to 0.35 is one half-life and 0.40 to 0.10 is two half-lives. K = 0.1066346 hr -1 (I kept some guard digits and will round off the time at the end.) If it takes 6.5 hours for the concentration of H 2O 2 to decrease from 0.70 to 0.35, how many hours are required for the concentration to decrease from 0.40 to 0.10 ? Problem #7: The decomposition of aqueous hydrogen peroxide to gaseous oxygen and water is a first-order reaction. Solution: 75% complete means 25% of A remains.ĥ17.5 comes from 69.8 min times 60 sec / min. Problem #6: A certain first-order reaction is 75% complete in 69.8 min. Set the first concentration to be A o and the second to be A. What is the rate constant for this reaction? Problem #5: The reactant concentration in a first-order reaction was 7.30 x 10 -2 M after 45.0 s and 8.70 x 10 -3 M after 65.0 s. This problem could have been done with A = 0.195 and A o = 1 Solution: 80.5% complete means 19.5% remaining. Assuming 0.0100 M, calculate the time in seconds required for the reaction to reach 80.5 percent completion. Gives a plot of ln vs time in seconds which is a straight line with a slope of -7.35 x10 -3. Note that the problem specified the amount remaining, not the amount decomposed.Ģ) Integrated form of first-order rate law: I will use the one with the guard digits in the next calculation. What is the rate constant for this reaction? At what time after initiation of the reaction of the reaction will 10.0% of the reactant remain? seconds after initiation of the reaction, 32.5% of the reactant remains. Problem #3: A certain reaction is first order, and 540. K = 0.0091975 s -1 (I kept a few guard digits for the next calculation.) Determine the rate constant and the half-life for this process.ġ) Integrated form of first-order rate law: Problem #2: A certain first order reaction is 45.0% complete in 65 s. You must have the rate constant in order to get the half-life, so that calculation must be done, regardless of the question asking for it or not. Note that this question does not ask for the rate constant. It is very common for the question to give you how much is used up and remain silent that you must use how much remains. Note that this calculation is done with how much substance remains, not how much is used up. Problem #1: Calculate half-life for first-order reaction if 68% of a substance is reacted within 66 s. ChemTeam: Kinetics: first-order chemical reactions
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