15. Chemical Kinetics

Half-Life

15. Chemical Kinetics

Half-Life

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Half-life of a second-order reaction | Kinetics | Chemistry | Khan Academy

07:09

Half-life of a second-order reaction | Kinetics | Chemistry | Khan Academy

Khan Academy Organic Chemistry

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08:47

Kinetics: The Half Life

Half-life of a first-order reaction | Kinetics | AP Chemistry | Khan Academy

Khan Academy Organic Chemistry

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16:06

Kinetics of Radioactive Decay

14.5 Integrated Rate Laws | General Chemistry

Chad's Prep

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Practice this topic

Multiple Choice

Decomposition of a certain substance Y at 45°C was found to be zero order. What is the half-life of substance Y if it took 15.5 minutes to decompose 67% of this substance? [Y]₀ = 0.25 M.

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Multiple Choice

Radioactive plutonium-239 (t_1/2 = 2.41 × 10⁵ yr) is used in nuclear reactors and atomic bombs. If there are 5.70 × 10² g of plutonium isotope in a small atomic bomb, how long will it take for the substance to decay to 3.00 × 10² g?

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Multiple Choice

Use the data below to determine the half-life of decomposition of NOCl reaction which follows 2nd order kinetics.

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Multiple Choice

The conversion of methyl isonitrile into acetonitrile follows first-order kinetics with a half-life of 110.2 seconds. What mass of a 1.00-g sample of methyl isonitrile remains after 10.0 minutes?

CH₃ – N≡C → CH₃ – C≡N

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Multiple Choice

What is the half-life of a second-order reaction in which 45.0% of the original concentration of 1.00 M remains after 325 seconds?

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Textbook Question

Given the following diagrams at t = 0 min and t = 30 min

After four half-life periods for a first-order reaction, what fraction of reactant remains? [Section 14.4]

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Textbook Question

Consider the first-order decomposition of A molecules (red spheres) in three vessels of equal volume. (1)-(3)

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Textbook Question

Consider the first-order decomposition of A molecules (red spheres) in three vessels of equal volume. (1)-(3)

(b) What are the relative half-lives of the reactions in vessels (1)–(3)?

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Textbook Question

(a) The gas-phase decomposition of SO2Cl2, SO2Cl21g2 ¡SO21g2 + Cl21g2, is first order in SO2Cl2. At 600 K the half-life for this process is 2.3 * 105 s. What is the rate constant at this temperature?

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Textbook Question

Consider the first-order reaction AS B in which A molecules (red spheres) are converted to B molecules (blue spheres).

(a) Given the pictures at t = 0 min and t = 1 min, draw pictures that show the number of A and B molecules present at t = 2 min and t = 3 min.

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Textbook Question

The first-order rate constant for the decomposition of N2O5, 2 N2O51g2¡4 NO21g2 + O21g2, a t 70 C i s 6.82 * 10-3 s-1. Suppose we start with 0.0250 mol of N2O51g2 in a volume of 2.0 L. (c) What is the half-life of N2O5 at 70 C ?

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Textbook Question

From the following data for the first-order gas-phase isomerization of CH3NC at 215 C, calculate the firstorder rate constant and half-life for the reaction: Time (s) Pressure CH3nC (torr) 0 502 2000 335 5000 180 8000 95.5 12,000 41.7 15,000 22.4

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Textbook Question

Consider the data presented in Exercise 14.19. (c) What is the half-life for the reaction?

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Textbook Question

The decomposition of XY is second order in XY and has a rate constant of 7.02 * 10 - 3 M- 1 # s - 1 at a certain temperature. a. What is the half-life for this reaction at an initial concentration of 0.100 M?

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Textbook Question

The half-life for the radioactive decay of U-238 is 4.5 billion years and is independent of initial concentration. How long will it take for 10% of the U-238 atoms in a sample of U-238 to decay?

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Textbook Question

The half-life for the radioactive decay of U-238 is 4.5 billion years and is independent of initial concentration. If a sample of U-238 initially contained 1.5 * 1018 atoms when the universe was formed 13.8 billion years ago, how many U-238 atoms does it contain today?

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Textbook Question

The half-life for the radioactive decay of C-14 is 5730 years and is independent of the initial concentration. How long does it take for 25% of the C-14 atoms in a sample of C-14 to decay?

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Textbook Question

The half-life for the radioactive decay of C-14 is 5730 years and is independent of the initial concentration. If a sample of C-14 initially contains 1.5 mmol of C-14, how many millimoles are left after 2255 years?

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Textbook Question

What is the half-life (in minutes) of the reaction in Problem 14.74 when the initial C4H6 concentration is 0.0200 M? How many minutes does it take for the concentration of C4H6 to drop from 0.0100 M to 0.0050 M?

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Textbook Question

The tabulated data were collected for this reaction at 500 °C: CH3CN(g)¡CH3NC( g) Time (h) [Ch3Cn] (M) 0.0 1.000 5.0 0.794 10.0 0.631 15.0 0.501 20.0 0.398 25.0 0.316 b. What is the half-life for this reaction (at the initial concentration)?

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Textbook Question

Trans-cycloheptene 1C7H122, a strained cyclic hydrocarbon, converts to cis-cycloheptene at low temperatures. This molecular rearrangement is a second-order process with a rate constant of 0.030 M-1 s-1 at 60 °C. If the initial concentration of trans-cycloheptene is 0.035 M: (c) What is the half-life of trans-cycloheptene at an initial concentration of 0.075 M?

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Textbook Question

Consider two reactions. Reaction (1) has a constant halflife, whereas reaction (2) has a half-life that gets longer as the reaction proceeds. What can you conclude about the rate laws of these reactions from these observations?

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Textbook Question

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Textbook Question

The desorption (leaving of the surface) of a single molecular layer of n-butane from a single crystal of aluminum oxide is found to be first order with a rate constant of 0.128>s at 150 K. b. If the surface is initially completely covered with n-butane at 150 K, how long will it take for 25% of the molecules to desorb (leave the surface)? For 50% to desorb?

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Textbook Question

The evaporation of a 120-nm film of n-pentane from a single crystal of aluminum oxide is zero order with a rate constant of 1.92 * 1013 molecules>cm2 # s at 120 K. a. If the initial surface coverage is 8.9 * 1016 molecules>cm2, how long will it take for one-half of the film to evaporate?

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Textbook Question

Americium-241 is used in smoke detectors. It has a first-order rate constant for radioactive decay of k = 1.6 * 10-3 yr-1. By contrast, iodine-125, which is used to test for thyroid functioning, has a rate constant for radioactive decay of k = 0.011 day-1. (b) Which one decays at a faster rate?

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Textbook Question

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Textbook Question

The rate of a first-order reaction is followed by spectroscopy, monitoring the absorbance of a colored reactant at 520 nm. The reaction occurs in a 1.00-cm sample cell, and the only colored species in the reaction has an extinction coefficient of 5.60 * 103 M-1 cm-1 at 520 nm. (c) Calculate the half-life of the reaction.

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Textbook Question

Anthropologists can estimate the age of a bone or other sample of organic matter by its carbon-14 content. The carbon-14 in a living organism is constant until the organism dies, after which carbon- 14 decays with first-order kinetics and a half-life of 5730 years. Suppose a bone from an ancient human contains 19.5% of the C-14 found in living organisms. How old is the bone?

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Textbook Question

The half-life for radioactive decay (a first-order process) of plutonium- 239 is 24,000 years. How many years does it take for one mole of this radioactive material to decay until just one atom remains?

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Textbook Question

The half-life for the first-order decomposition of N2O4 is 1.3 * 10-5 s. N2O41g2S 2 NO21g2 If N2O4 is introduced into an evacuated flask at a pressure of 17.0 mm Hg, how many seconds are required for the pressure of NO2 to reach 1.3 mm Hg?

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