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CHM2046 > Topic 24: Nuclear Chemistry > Flashcards

Topic 24: Nuclear Chemistry Flashcards

1
Q

Characteristics of chemical reactions (6)

A

a) Atoms never change their identity
b) e- in orbitals are involved
c) Nuclear particles do not take part
d) Relatively small changes in energy
e) No measurable changes in mass
f) Rate influenced by several external factors

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2
Q

Characteristics of nuclear reactions (4)

A

a) Atoms converted into atoms of another element
b) e- in orbitals are less involved
c) Nuclear particles are involved
d) Relatively large changes in energy
e) Measurable changes in mass
f) Rate depends on number of nuclei and rarely in the compound in which an element occurs

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3
Q

Nucleons

A

Protons + Neutrons

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4
Q

Nuclide definition

A

Nucleus with specific numbers of nucleons

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5
Q

Notation for nuclide

A

(Z/A)X
(1/1)p
(-1/0)e
(0/1)n

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6
Q

Naming of nuclide

A

Element name followed by the mass number

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7
Q

Radioactivity definition

A

Spontaneous disintegration of a nucleus by emitting radiation

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8
Q

Role of Becquerel in nuclear chemistry

A

Discovery of radiation in a photographic plate exposed to U
Radiation creates an electric discharge in the air

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9
Q

Role of Curie in nuclear chemistry

A

a) Intensity directly proportional to the concentration of the element in the mineral, not to the formula of the mineral or compound
b) Unaffected by physical/chemical conditions
c) Discovery of Po/Ra

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10
Q

Types of radioactive emission

A

a) Alpha particles - α | (2/4)He
b) Beta particles - β
c) Gamma rays - γ

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11
Q

Principles of radioactive decay

A

When a nuclide decays, it becomes a nuclide of lower energy
Excess energy is carried off by the emitted radiation and the recoiling nucle

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12
Q

Definition of parent/daughter nuclide

A

Decaying nuclide = Parent
Product nuclide = Daughter

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13
Q

Conservation principle of nuclear equations

A

(TotalZ/TotalA) Reactants = (TotalZ/TotalA) Products

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14
Q

α decay description
a) A = -4
b) Z = -2
c) N = -2

A

a) Emission of α particles
b) Most common means for heavy, unstable nucleus (Z=83) to become more stable

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15
Q

β- decay description
a) A = 0
b) Z = +1
c) N = -1

A

Emission of β- particles

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16
Q

Positron emission
a) A = 0
b) Z= -1
c) N = +1

A

Emission of β+ (antiparticle of e-)

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17
Q

e- capture
a) A = 0
b) Z= -1
c) N = +1

A

a) Nucleus draws in an e- from a low atomic energy level
b) Usually accompany by the release of x-ray or neutrinos

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18
Q

γ decay

A

a) γ emission accompanies other (β^-) modes of decay
b) γ rays emitted when a particle and an antiparticle annihilate each other
=> β+ + e- → 2γ
c) γ rays have no mass or charge

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19
Q

General factors that affect nuclear stability

A

a) Total mass of the nuclide
b) Ratio of (N/Z)

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20
Q

Band of stability (N/Z Graph)

A

a) Lighter nuclides are stable when N = Z
b) As Z increases, the N/Z for stable nuclei gradually increases
c) All nuclides with Z > 83 are unstable
d) Pairing of spins of like nucleons lead to greater stability

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21
Q

Exceptions to instable light nuclides

A

(1/1)H and (2/3)He

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22
Q

Magic numbers

A

2, 8, 20, 28, 50, 82, 126

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23
Q

Effect of strong force

A

a) Electrostatic repulsive forces between protons would break the nucleus if not for strong force
b) Strong force operates over short distances within the nucleus

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24
Q

Type of emission in
a) Neutron-rich nuclides (Higher than atomic mass)
b) Proton-rich nuclides (Lower than atomic mass)
c) Heavy nuclides (Beyond 83)

A

a) B- decay
b) B+ emission / e- capture
c) Alpha decay

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25
Q

Decay series definition

A

Series of decay steps before a stable daughter nuclide form

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26
Q

Principle for detecting radioactivity

A

Observing the effects of radioactive emission on the surrounding atoms

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27
Q

Methods used to detect and measure radioactivity

A

a) Ionization counter (Geiger-Muller)
b) Scintillation

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28
Q

Mechanism of ionization counter

A

a) Detect radioactive emissions as these cause gas (Ar) ionization
b) Ionized gaseous cations (Ar+) and free e- are attracted to electrodes from a recording device
c) Current created is amplified and appears as a meter reading

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29
Q

Structure of Geiger-Muller counter

A

Tube filled with Ar-CH4 mixture
a) Cathode (-) - Tube shell
b) Anode (+) - Central wire

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30
Q

Scintillation counter mechanism

A

a) Detect radioactivity emissions by their ability to excite atoms and make them emit light
b) Putting a radioactive sample into a liquid (phosphor)
c) Incoming radioactive particle strike the phosphor
d) Each photon strikes the cathode, releasing an e-
e) # of pulses proportional to the concentration of the radioactive substance

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31
Q

Does the rate of radioactive decay depend on the chemical substance?

A

No

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32
Q

Decay rate / activity definition

A

Change in # of nuclei divided by the change in time

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33
Q

Calculation of decay rate

A

A = - ∆N/∆t

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34
Q

Units of decay rate

A

1Bq = 1d/s (SI)
1Ci = 3.7x10^10 d/s

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35
Q

What order kinetics does the decay rate follow?

A

First order kinetics (A = kN)
ln(No/Nt) = kt

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36
Q

Half-life equation

A

Time taken for half the nuclei in a sample to decay
a) t(1/2) = ln⁡(2)/k

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37
Q

Radioisotope dating purpose

A

Determine the ages of certain objects

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38
Q

Radiocarbon dating

A

Measure relative amounts of C-14 and C-12 in materials of biological origin (36000yrs)
a) Ratio remains the same for all living organisms
b) Once the organism dies, the amount of C-14 starts to decrease as it decays
c) Measuring its amount present indicates the time that has passed

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39
Q

Formula for radiocarbon dating

A

(1/k) ln(A0/At) = t
A0 = Activity in living organism
At = Activity in object whose age is unknown

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40
Q

Nuclear transmutation definition

A

a) Induced conversion of the nucleus of one element into the nucleus of another
b) Achieved by high-energy bombardment of nuclei in a particle accelerator

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41
Q

Notation for nuclear transmutation

A

Reactant nucleus (Particle in, Particle(s) out) Prdouct nucleus

42
Q

Characters that contributed to nuclear transmutation

A

a) Rutherford bombarded the N with a particles to form O
b) Chadwick discovered the neutron by bombarding Li with a particles
c) Irene and Frederic created the first artificial radioisotope.

43
Q

Particle accelerator principle

A

Imparting high KE to particles by placing them in an electric field with a magnetic field

44
Q

Linear accelerator

A

a) Series of separated tubes increasing in length with alternating voltage
b) Particle is accelerated from one tube to the next by repulsion/attraction

45
Q

Cyclotron (Lawrence, 1930)

A

a) Use of electromagnets to give the particle a spiral path to save space
b) Same principle as linear accelerator

46
Q

Synchrotron

A

Synchronously increasing magnetic field to make particle’s path circular

47
Q

Large Hadron Collider

A

World’s most powerful accelerator
First successful collision of protons

48
Q

Application of particle accelerators

A

a) Production of radioisotopes used in medical field
b) Synthesis of transuranium elements (higher atomic number than U)

49
Q

What do nuclear changes cause?

A

a) Chemical changes in surrounding matter
b) Ionization in surrounding matter (Cation + e- pair)

50
Q

What is the relationship between incoming energy and the number of cation-electron pairs?

A

Directly proportional

51
Q

General principle of the penetrating power of a particle

A

If a particle interacts strongly with matter, it penetrates only slightly.

52
Q

Ionizing ability and penetrating power of a particle

A

a) Interact with matter most strongly
b) Piece of paper can stop radiation from external source

53
Q

Ionizing ability and penetrating power of B particle

A

a) Interact less strongly with matter
b) Thick piece of metal is required to stop these particles

54
Q

Ionizing ability and penetrating power of γ particle

A

a) Interact least with matter and penetrate most
b) Block of Pb several inches thick is needed to stop them

55
Q

Factors that affect the danger from a radioactive nuclide

A

a) Type of radiation
b) Half-life of the radioactive nuclide
c) Biological behavior of the radioactive nuclide

56
Q

Explanation of the biological behavior of the radioactive nuclide

A

a) Sr-90 (Similar to Ca and easily absorbed by bones)
b) Water is the most likely molecule to absorb γ radiation

57
Q

Reaction of water after absorbing y radiation

A

H2O + γ → H2O∙ + e-
Products collide with other water molecules to form more free radicals
Free radicals are unstable and extremely reactive
Attacking the bonding and structure of surrounding molecules

58
Q

Units of energy absorption

A

SI: 1 Gy = 1 J/kg
Common: 1 rad = 0.01 Gy

59
Q

Definition of Rem

A

Unit of radiation dosage equivalent to a given amount of tissue damage
A) no. of rems = rads x RBE

60
Q

SI Units of tissue damage

A

1 Sv = 100 rem

61
Q

Sources of ionizing radiation

A

a) Cosmic radiation
b) Th and U minerals present in soil
c) Medical diagnostic techniques
d) Radioactive waste disposal
e) Radioactive K-14 in daily intake of food/tap water

62
Q

Explanation of radiation in Rn

A

Production of Rn from Th and U minerals present in soil
Cause of lung cancer

63
Q

What factors influence the risk from ionizing radiation?

A

Increase in the cancer incidence from
a) High, single exposure
b) Low chronic exposure

Ex. Fruit flies with genetic defects (Linear)

64
Q

Models for assessing ionizing radiation

A

a) Linear response - Radiation effects accumulate over time
b) S-shaped response - Threshold above which effects are more significant

65
Q

Principles of radioactive tracers

A

Tiny amount of a radioisotope mixed with large amount of stable isotope of the same element

66
Q

Applications of radioactive tracers

A

a) Reaction pathways
=> Periodate-iodide reaction
=> Photosynthesis
b) Physiological studies
=> I-125 labeled albumin
=> Cr-51 labeled RBC
c) Material flow
=> Semiconductor chips and metal plating
=> Map of water flow from land to lakes

67
Q

Neutron activation analysis

A

a) Converting a small fraction of its atoms to radioisotopes
b) Exhibition of a characteristic decay pattern that reveals the elements present

68
Q

Medical diagnosis with radioisotopes

A

a) Production of an image of the thyroid gland with I-131
b) Positron-emission tomography
=> Imaging method for observing brain structure and function
=> Injected substance in bloodstream emits positrons annihilated by e-

69
Q

Applications of radioisotopes

A

a) Radiation therapy with Au/Sr (Interference with cell division)
b) Destruction of microbes (Killing organisms that cause rotting)
c) Insect control
d) Power for spacecraft instruments

70
Q

Types of nuclear processes

A

a) Fission (Heavy nucleus splits into two)
b) Fusion (Lighter nuclei combine to form one)
c) Decay (Emission of few small particles to become a more stable lighter nucleus)

71
Q

Conservation principle for nuclear reactions

A

Total quantity of mass-energy in the universe is constant
E = mc^2

72
Q

Mass difference in nuclear reactions

A

There is always a mass decrease when nucleons form a nucleus
a) Decrease in mass is due to mass being converted to energy to hold the nucleus together (Mass effect)

73
Q

Definition of nuclear binding energy

A

Energy required to break 1 mol of nuclei of an element into individual nucleons

74
Q

eV Unit

A

Energy an electron acquires when it moves through a potential difference of 1 V

75
Q

Binding energy per nucleon

A

BE/n = (Binding energy) / (No of nucleons)

76
Q

Relationship between binding energy per nucleon and nuclear stability

A

The greater the binding energy per nucleon, the more stable the nuclide is

77
Q

The role of fission and fusion in binding energy per nucleon

A

Binding energy per nucleon peaks at element with A = 60
a) Fission - A heavier nucleus that can split into lighter nuclei (closer to A = 60)
b) Fusion - Lighter nuclei can combine to form a heavier nucleus

78
Q

Historical context of fission

A

a) Enrico Fermi bombarded U with n
b) Otto Han found an isotope of Ba in sample
c) Meitner proposed fission model to explain this

79
Q

General process of fission reaction

A

a) Neutron bombardment results in a highly excited U-236
b) Process is harnessed by chain reaction

80
Q

Description of chain reaction during fission

A

a) Few neutrons that are released by the fission of one nucleus collide with other fissionable nuclei and cause them to split
b) This releases more neutrons in a self-sustaining process
c) Each event in a chain reaction releases about 2.5 times as much energy as the preceding one

81
Q

Definition of critical mass

A

Mass required to achieve a chain reaction

82
Q

How does an atomic bomb work?
a) Manhattan Project (1941)
b) Detonation of 2 (1945)

A

a) Small explosions of TNT bring subcritical masses of fissionable material together to exceed the critical mass and ensuing chain reaction brings about the explosion

83
Q

Principle of nuclear energy reactor

A

Generate heat to produce steam, turning a turbine attached to an electric generator

84
Q

Where does heat generation occur?

A

Reaction core

85
Q

Elements of nuclear energy reactor

A

a) Fuel rods
b) Control rods
c) Reflector
d) Moderator

86
Q

Fuel rods
a) Composition
b) Function

A

a) Fuel (U-235) enclosed in tubes of a corrosion-resistant Zr alloy
b) Release of neutrons

87
Q

How are fuel rods enriched with U-235 3% / 4%?

A

Gas centrifugation / Graham law

88
Q

Control rods
a) Composition
b) Function

A

a) Made up of Cd / B absorb neutrons efficiently
b) Regulate nuclear activity

89
Q

Reflector
a) Composition
b) Function

A

a) Made up of Be
b) Absorb very few neutrons and reflect those back to fuel rods

90
Q

Moderator
a) Composition
b) Function

A

a) H2O (Light) / D2O (Heavy)
b) Slows the neutrons, making them much better for fission / Acts as a coolant by transferring heat to the steam producing region

91
Q

Advantages of heavy water reactors

A

a) Absorbs very few neutrons
b) Use U that has been less enriched

92
Q

Breeder reactors principles and disadvantages (Not longer used in the US)

A

Consume one type of nuclear (U-238) fuel as it produces another (Pu-239) by neutron release
Difficult and expensive to build
Products are extremely toxic

93
Q

Power plant accidents (3)

A

1979 - Malfunctions of coolant pumps and valves in Pennsylvania
1986 - Cooling system failure at the Chernobyl plant in Ukraine
2011 - Destruction of Fukushima nuclear facility by Tsunami, melting 3 reactors

94
Q

Use of nuclear reactors in Europe

A

Important source of electricity due to climate change policies
Germany committed to closing all its nuclear power plants by 2022

95
Q

Thermal and waste pollution in nuclear reactors

A

a) Water used to condense the steam is several degrees warmer when returned to its source, which can harm aquatic organisms
b) Many of the fission products formed in nuclear reactors have long half-lives, and no plan for their permanent disposal has yet been devised.

96
Q

How were all elements heavier than H formed in the stars?

A

Fusion and decay processes

97
Q

Example of fusion reaction to produce He

A

H-2 + H-3 → He-3 + n-1

98
Q

Benefits and disadvantages of He fusion reaction from tritium

A

a) Enormous quantity of energy with no radioactive byproducts
b) Tritium is scarce and only produced in cosmic radiation or nuclear accelerators by bombarding Li

99
Q

Complication of fusion reactions

A

Require enormous energy (heat) to give the + charged nuclei enough KE to force themselves together

100
Q

Solutions to fusion complication

A

a) Atoms are stripped of their e- at high temperatures that results in a gaseous plasma enclosed within a magnetic field (Tokamak)
b) Using many focused lasers to compress and heat the fusion reactants

CHM2046 (8 decks)

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