U1 S1 L5 Application of Collision Theory

Upon completion of this lesson, you will be able to: analyse and describe examples where technologies were developed based upon scientific understanding. analyse and describe examples where scientific understanding was enhanced or revised as a result of the invention of a technology. identify and describe science and technology based careers.

Smog Smog is a word that was invented about 100 years ago. – Smog refers to a condition that arises when smoke emissions are mixed with moist foggy air. It is properly called photochemical smog and it is easily identified by a hazy, yellow-brown sky. It is a form of air pollution resulting from the action of sunlight on nitrogen oxide (NO x ) and hydrocarbon emissions from automobiles. Smoggy air contains CO, NO, NO 2, C x H y, and O 3. On smog alert days, breathing is uncomfortable, and the sky is in a word ugly. Of particular interest in smog is ozone. –Ground level ozone, O 3, forms when the nitrogen monoxide from vehicle exhaust combines with O 2 in the air.

Smog Reaction Mechanism Identify all : 1) intermediates2) Catalysts

You might be thinking ozone production "isn't that good?“ –in the upper atmosphere, ozone absorbs ultraviolet (uv) light thereby protecting life on earth from the dangerous effects of uv light. (That’s good!) –but at ground level it irritates the respiratory tract and eyes, increases the risk of heart or lung disease, causes plant leaves to become brittle, bleaches colour from fabrics, and breaks down the elasticity of rubber. Ozone is a nasty chemical at ground level! The question becomes: how do we deal with it? –Based on the mechanism provided above, one way of preventing ozone formation at ground level is to get rid of the catalyst for the production of monoxygen.

The Catalytic Converter Modern catalytic converters have two purposes. 1.One is to convert carbon monoxide and nitrogen monoxide to nitrogen and carbon dioxide. 2.The other is to convert unburned hydrocarbons (which are responsible for PAN's - another component of smog) to carbon dioxide and water –There are several different designs of catalytic converters on the market. The actual catalysts vary from one to another. –Some of the more common catalysts are: palladium, platinum, rhodium, nickel(III) oxide, copper(I) oxide, and chromium(III) oxide. –The internal design maximizes the surface area available for contact between the exhaust gases from the engine and the metal or metal oxide catalysts

Reaction Mechanism using catalyst

Lead and Catalytic Converters Leaded gasoline molecules have four ethyl (CH3CH2-) groups bonded to a central lead atom. They burn evenly in car engines reducing a condition called knock - which is associated with burning straight chain alkanes. 1.The use of leaded gasoline was phased out and eventually banned by 1990 in Canada. The main reason for the ban is the poisonous effects of lead. 2.A second reason for its elimination was its effect on the efficiency of catalytic converters. Lead not only poisons people, it also "poisons" converters by binding to the catalysts. Once it becomes covered in an impurity like lead, a converter can no longer adsorb CO and NO molecules.

MTBE and Branched Hydrocarbons The replacement for leaded gasoline molecules are highly branched hydrocarbons like 2,2,4-trimethylpentane. However, the need for oxygen in gasoline has lead to the use of an ether called methyl tert-butyl ether or MTBE. It provides more oxygen to the combustion reaction and helps increase the amount of oxygen going into the converter to get rid of unburned hydrocarbons. MTBE is currently at the center of a controversy. In gas tanks, MTBE is not a real problem, but in ground water and wells it is because it is a suspected carcinogen (cancer causing agent). It is finding its way into water supplies in cities and towns throughout North America because of sloppy filling practices and gasoline spills.

Handout: Smog, Catalytic converters and You. Textbook Readings MHR page 802: Automobile Engines (paragraph 1) Textbook Practice Items MHR page 487: item 19