4.4-4.5: Chain Reactions & Photochemistry Flashcards

1
Q

Free radicals (⦁)

A

atoms/molecules w/ unpaired e-

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2
Q

are free radical highly reactive

A

YES- w/ short life

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3
Q

how do free radicals gain stability?

A

Gains stability by pairing w/ e- on another atom (covalent bonding)

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4
Q

Free radical formation reaction

A

(⦁) forms new bond at expense of already existing bond
- New radical attacks another molecule, forms new radical
- A⦁ + B-C –> A-B + C⦁

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5
Q

Chain termination reaction

A

pair of radicals find each other = form stable molecule
- A⦁ + C⦁  A-C

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6
Q

Catalyzed chain reaction

A

radical chain reaction circumvents kinetic barrier

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7
Q

Initiation event

A

produces initial population of radicals
- Required to start radical reactions
- Somehow bond breaks –> fragments of unpaired e-

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8
Q

Atmospheric chemistry is governed by ___ produced by ____

A
  • free radicals
  • solar radiation
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9
Q

NOx is an exception to free radicals bc…

A

it’s still stable (even though has unpaired e-) bc… unpaired e- = in low-energy molecular orbit

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10
Q

Spectrum

A

variation of light intensity w/ wavelength

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11
Q

spectrum: visible light

A

wavelength = 400-750 nm (violet –> red)

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12
Q

spectrum: ultraviolet light (UV)

A

wavelength = < 400 nm

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13
Q

spectrum: infrared light (IR)

A

wavelength = > 750 nm

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14
Q

Most of suns rays = w/in _______ light region

A

visible

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15
Q

Solar Spectrum:

A

Records light arriving @ earth’s surface on clear day
- Sun emits more UV-rays (absorbed by stratospheric ozone layer)

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16
Q

Photon

A

energy packets (how light rays are delivered)

17
Q

how light rays are delivered?

A

photons

18
Q

relationship b/w energy of photon and frequency of light

A

Energy of photon = proportional to frequency of light

19
Q

relationship b/w light and wavelength

A

inversely proportional

20
Q

E =

A

hv = (hc)/ƛ

21
Q

h =

A

Planck’s constant = 6.626 x 10-34 J*sec

22
Q

c =

A

speed of light = 2.998 x 108 m/s

23
Q

When 1 mol photons = absorbed: energy deposited in molecules (E) =

A

(119.627/ƛ)

24
Q

visible light/UV light absorption occurs when…

A

energy is sufficient to raise molecule (ground state) –> (excited state)

25
Q

molecules release their extra/excited energy by..

A
  • re-emit photon
  • collide w/ other molecule and transfer kinetic energy
  • break bond releasing pair of e- fragments
26
Q

for a bond to break: the energy absorbed by photon ___ bond energy

A

energy (absorbed photon) ≥ bond energy

27
Q

Why are free radicals so reactive?

A

Bc of unpaired e-

28
Q

How do radical chain reactions terminate?

A

When a pair of radicals find each other = form stable molecule
- A⦁ + C⦁  A-C

29
Q

What are the requirements for a radical reaction to take place?

A
  1. Present in low concentrations so must encounter another free radical
  2. Initiation event- produces initial population of radicals
    - Somehow bond breaks –> fragments of unpaired e-
30
Q

What is the role of sunlight in atmospheric radical reactions?

A

Atmospheric chemistry = governed by free radicals produced by solar radiation
- (⦁) reacts w/ nitric oxide  NO2⦁ + sunlight = splits + O2 = ozone

31
Q

Where is the solar spectrum strongest?

A

Wavelength (ƛ) ≈ 483 nm

32
Q

In what region of the electromagnetic spectrum does the sun’s radiation occur?

A

Mostly visible light region (some/tails off at infrared and ultraviolet)

33
Q

How does sunlight react with molecules in the atmosphere?

A

Sunlight = delivered in photons
- Ultraviolet ƛ = splits O2 (O⦁ *2)
- O⦁ = energetically excited + O2 = bonds to form O3 (ozone)