± Half-life (kinetics) for First Order Reactions < 10 of 18> I Review | Constants | Periodic Table Half-life equation for first-order reactions: The integrated rate law allows chemists to predict the reactant concentration after a certain amount of time, or the time it would take for a certain concentration to be 0.693 reached. where t2 is the half-life in seconds (s), and k is the rate constant inverse seconds (s1) The integrated rate law for a first-order reaction is: [A] = [A]oe Part A Now say we are particularly interested in the time it would take for the concentration to become one-half of its initial JA What is the half-life of a first-order reaction with a rate constant of 7.40x10-4 s12 value. Then we could substitute for [A] and rearrange the equation to: Express your answer with the appropriate units. > View Available Hint(s) 4/2 = 0.603 This equation calculates the time required for the reactant concentration to drop to half its initial value. In other words, it calculates the half-life, ? Value Units

The following reaction is first order in respect to CH3OH and first order in respect to HCl.  With this in mind, what is the rate constant for the reaction?  Be sure you choose the answer with the right units.   CH3OH(aq) + HCL(aq) ---->  CH3CL(aq)  + H2O(i) Reaction CH3OH conc. HCl conc. Initial Rate (M/s) 1 0.100 M 0.100 M 1.1 x 10-2

Nitrification is a biological process for removing NH3 from wastewater as NH4+: NH, +20, → NO3 + 2H + H2O The first-order rate constant is given as k₁ = 0.47e0.095(T-15°C) where k₁ is in day¹ and T is in °C. If the initial concentration of NH3 is 3.0 mol/m³, how long will it take to reduce the concentration to 0.66 mol/m³: (a) in the spring (T = 20°C)? days (b) in the winter (T = 10°C)? days

The following data show the rate constnat of a first order reaction measured at several different temperatures. Construct and Arrhenius plot (ln k vs 1/T) to determine the activation energy (Ea). You should use a graphing program like excel to construct your graph. A sketch of the graph including the equation of the line should be included in your notebook.    temperature (K) rate constant (s-1) 375 1.68 x 10-5 400 3.50 x 10-5 500 4.20 x 10-4 600 2.11 x 10-3

Consider a first-order decomposition of the substance A. It takes 60 min ufor the concentration of A to drop to half its initial value. How long, in total, will it take for the concentration of A to fall from its initial value to 12.5%? Select one: 1. 45 min 2. 15 min 3. 180 min 4. 120 min 5. None of the other answers

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Q7

Your laboratory is asked to analyze a water sample for a particular pesticide. You know from previous study that this pesticide degrades via a first order, irreversible reaction. The first order rate constant (k) for the reaction at 4 °C is 0.02 day¹. The activation energy for the reaction is known to be 10 kcal/mol. The standard preservation method for water samples containing this pesticide is to store the sample at 4 °C for no more than 24 hours prior to analysis. Calculate the fraction of the pesticide that remains in the sample after 24 hours of storage at 4 °C. b. A newly hired staff member collects a sample of the water but forgets to store it at 4 °C. Instead, they leave the sample in the trunk of their car (average temperature 35 °C) over the weekend. 60 hours later the sample is analyzed and found to contain 0.01 mg/L of the pesticide. What was the pesticide concentration in the water at the time the sample was taken?