Chapter 13 HW

1) C 2) E 3) A 4) D 5) B

Place in order for the formation of smog 1-5. A) An alkyl peroxyl radical, ROO: is produced B) Particles in the atmosphere obscure visibility C) NO and another product are produced from NO2 D) NO reacts to produce NO2 E) an alkyl Radical, R:, is produced from a hydrocarbon

HO: addes across the double bond in H2C=CH2 to produce an oxygenated free radical, H3C-CH2O. The hydroxyl radical abstracts a hydrogen atom from CH4 to produce a mythyl radical.

Show how hydroxyl radical, HO:, might react differently with ethylene, H2C=CH2 and methane.

This phenomenon probably indicates that small inorganic particles serve as condensation nuclei around which organic molecules formed in smog condense. The organic portion of the aerosol would not be hydrocarbon, but would consist of oxygenated organic species generated by the oxidizing conditions in photochemical smog.

Smog aerosol droplets are composed of organic matter surrounding a small inorganic core. Suggest what this shows regarding the process by which these aerosols are formed. is the organic portion of the aerosol likely to be pure hydrocarbon?

CO in the atmosphere is indicative of automobile exhaust pollution. However, it is oxidized rather readily in the presence of photochemical smog, which might make it an unreliable measure of hydrocarbon emissions.

Why might carbon monoxide be chosen as a standard against which to compare automotive hydrocarbon emissions in atmospheres where smog is formed? what are some pitfalls created by this choice?

By oxidation of I- to I3-

How might oxidants be detected in the atmosphere?

Because rates of reaction with hydroxyl radical are used to express reactivities.

Why is reactivity based on reaction with HO:?

Benzene can be the end product of the addition of HO to benzene.

Name the stable product that results from an initial addition reaction of hydroxyl radical HO with benzene?

SO2, would be found in a reducing smog; the other species occur in photochemical smog

Of the following species, the one most likely to be found in reducing smog is: ozone, relatively high levels of atomic oxygen, SO2, PAN, PBN

E) N

Of the following species, the one which is the least likely product of the absorption of a photon of light by a molecule of NO2? A) O B) a free radical species C) NO D) NO2* E) N

Propane would have to undergo an abstraction reaction, such as removal of an H atom by reaction with an O atom. Propene can also undergo abstraction reactions, but is more likely to undergo addition, particularly with HO: adding across a double bond.

Some atmospheric chemical reactions are abstraction reactions and others are addition reactions. Which of these applies to the reaction of hydroxyl radical with propane? with propene?

A reactive species has a strong tendency to react but, in the absence of some species with which to react, it might be relatively stable. An unstable species is one that tends to gain stability by undergoing some sort of process on its own. Sulfur dioxide is stable for some time in the atmosphere in the absence of oxidants such as those present in photochemical smog in which case it undergoes rapid oxidation. Excited nitrogen dioxide, NO2*, is unstable and readily emits a photon to revert to ground-state NO2.

What is the distinction between reactivity and instability as applied to some of the chemically active species in a smog-forming atmosphere?

Organic peroxy radicals, ROO:, oxidize NO to NO2 in a smoggy atmosphere

What is the main species responsible for the oxidation of NO to NO2 in a smoggy atmosphere?

A lean mixture tends to promote formation of nitrogen oxides.

What pollution problem does a lean mixture aggravate when employed to control hydrocarbon emissions from an internal combustion engine?

B) RO: is a free radical

Which of the following statements are true: A) RO: reacts with NO to from alkyl nitrates B) RO: is a free radical C) RO: is not a very reactive species D) RO: is not thought to be a n intermediate in the smog-forming process

Automotive exhaust pollutant hydrocarbons contain a relatively high proportion of unsaturated alkenes, which readily react in the atmosphere to produce photochemical smog.

Why are automotive exhaust pollutant hydrocarbons even more damaging to the environment than their quantities would indicate?

it is called a three way conversion catalyst because a single catalytic unit destroys all three of the main classes of automobile exhaust pollutants - hydrocarbons, carbon monoxide and nitrogen oxides.

Why is a modern automotive catalytic converter called a "three-way conversion catalyst?"

NO2 is, itself, a radical species with an unpaired electron.

Why is it that, NO2 can react with free radical species to terminate chain reactions involved in smog formation?

Ozone is damaging to rubber because of its strong tendency to add across double bonds in the rubber polymer causing the rubber to become brittle.

Why is ozone especially damaging to rubber?