15. Chemical Kinetics

Half-Life

15. Chemical Kinetics

# Half-Life - Video Tutorials & Practice Problems

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**Half-Life** is the time it takes for *half *of a reactant to *decay* in a certain time period.

Understanding Half-Life

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concept

## Half-Life Concept 1

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example

## Half-Life Example 1

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Problem

ProblemDecomposition 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.

A

0.058 min

B

0.029 min

C

11.6 min

D

23.5 min

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concept

## Half-Life Concept 2

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example

## Half-Life Example 2

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Problem

ProblemRadioactive plutonium-239 (t_{1/2} = 2.41 × 10^{5} yr) is used in nuclear reactors and atomic bombs. If there are 5.70 × 10^{2} g of plutonium isotope in a small atomic bomb, how long will it take for the substance to decay to 3.00 × 10^{2} g?

A

2.23×10

^{5}yrB

2.60×10

^{5}yrC

517 yr

D

600 yr

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concept

## Half-Life Concept 3

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example

## Half-Life Example 3

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9

Problem

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

A

1.00×10^{4} s

B

1.80×10^{5} s

C

2.02×10^{4} s

D

1.022×10^{3} s

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PRACTICE PROBLEMS AND ACTIVITIES (29)

- Given the following diagrams at t = 0 min and t = 30 min After four half-life periods for a first-order react...
- Consider the first-order decomposition of A molecules (red spheres) in three vessels of equal volume. (1)-(3...
- Consider the first-order decomposition of A molecules (red spheres) in three vessels of equal volume. (1)-(3...
- (a) The gas-phase decomposition of SO2Cl2, SO2Cl21g2 ¡SO21g2 + Cl21g2, is first order in SO2Cl2. At 600 K the ...
- Consider the first-order reaction AS B in which A molecules (red spheres) are converted to B molecules (blue s...
- The first-order rate constant for the decomposition of N2O5, 2 N2O51g2¡4 NO21g2 + O21g2, a t 70 C i s 6.82 * 1...
- From the following data for the first-order gas-phase isomerization of CH3NC at 215 C, calculate the firstord...
- Consider the data presented in Exercise 14.19. (c) What is the half-life for the reaction?
- 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 certa...
- The half-life for the radioactive decay of U-238 is 4.5 billion years and is independent of initial concentrat...
- The half-life for the radioactive decay of U-238 is 4.5 billion years and is independent of initial concentrat...
- The half-life for the radioactive decay of C-14 is 5730 years and is independent of the initial concentration....
- The half-life for the radioactive decay of C-14 is 5730 years and is independent of the initial concentration....
- What is the half-life (in minutes) of the reaction in Problem 14.74 when the initial C4H6 concentration is 0....
- The tabulated data were collected for this reaction at 500 °C: CH3CN(g)¡CH3NC( g) Time (h) [Ch3Cn] (M) 0.0 1.0...
- Trans-cycloheptene 1C7H122, a strained cyclic hydrocarbon, converts to cis-cycloheptene at low temperatures. ...
- Consider two reactions. Reaction (1) has a constant halflife, whereas reaction (2) has a half-life that gets ...
- The desorption (leaving of the surface) of a single molecular layer of n-butane from a single crystal of alumi...
- The desorption (leaving of the surface) of a single molecular layer of n-butane from a single crystal of alum...
- The evaporation of a 120-nm film of n-pentane from a single crystal of aluminum oxide is zero order with a rat...
- Americium-241 is used in smoke detectors. It has a first-order rate constant for radioactive decay of k = 1.6 ...
- Americium-241 is used in smoke detectors. It has a first-order rate constant for radioactive decay of k = 1.6 ...
- The rate of a first-order reaction is followed by spectroscopy, monitoring the absorbance of a colored reactan...
- Anthropologists can estimate the age of a bone or other sample of organic matter by its carbon-14 content. The...
- The half-life for radioactive decay (a first-order process) of plutonium- 239 is 24,000 years. How many year...
- The half-life for the first-order decomposition of N2O4 is 1.3 * 10-5 s. N2O41g2S 2 NO21g2 If N2O4 is intro...
- How long will it take for the concentration of SO2Cl2 to decrease to 25% of its initial concentration?"
- What is the rate constant of a first-order reaction when 20.0% of a reactant remains after 30.0 s?
- What is the half-life for a particular reaction if the rate law is rate = (1301 min-1)[A]?