Page 290 - 9780077418427.pdf

/Users/user-f465/Desktop
tiL12214_ch10_251-274.indd Page 267 9/3/10 6:11 PM user-f465
tiL12214_ch10_251-274.indd Page 267 9/3/10 6:11 PM user-f465 /Users/user-f465/Desktop

Science and Society

The Catalytic Converter
he modern automobile produces two explains why chemical reactions proceed lowered. Some catalysts do this better with
Ttroublesome products in the form of at a faster rate at higher temperatures. some specific compounds than others,
(1) nitrogen monoxide and (2) hydrocar- At higher temperatures, molecules have and extensive chemical research programs
bons from the incomplete combustion of greater average kinetic energies; thus, they are devoted to finding new and more effec-
gasoline. These products from the exhaust already have part of the minimum energy tive catalysts.
enter the air to react in sunlight, eventually needed for a reaction to take place. Automobile catalytic converters use
producing an irritating haze known as photo- The rate at which a chemical reaction metals such as platinum and transition
chemical smog. To reduce photochemical proceeds is affected by a catalyst, a material metal oxides such as copper(II) oxide and
smog, modern automobiles are fitted with that speeds up a chemical reaction without chromium(III) oxide. Catalytic reactions
a catalytic converter as part of their exhaust being permanently changed by the reac- that occur in the converter can reduce or
system (Box Figure 10.1). tion. A catalyst appears to speed a chemical oxidize about 90 percent of the hydro-
Molecules require a certain amount reaction by lowering the activation energy. carbons, 85 percent of the carbon monoxide,
of energy to change chemical bonds. This Molecules become temporarily attached to and 40 percent of the nitrogen monoxide
certain amount of energy is called the ac- the surface of the catalyst, which weakens from exhaust gases. Other controls, such
tivation energy, and it represents an en- the chemical bonds holding the molecule as exhaust gas recirculation (EGR), are
ergy barrier that must be overcome before together. The weakened molecule is easier used to reduce further nitrogen monoxide
a chemical reaction can take place. This to break apart and the activation energy is formation.

Engine Tailpipe

Catalytic converter
Exhaust pipe
Muffler

A B
BOX FIGURE 10.1 (A) This silver-colored canister is the catalytic converter. (B) The catalytic converter is located between the engine and
the muffler, which is farther back toward the rear of the car.

CONCEPTS Applied

TABLE 10.1
Household Chemistry
Three interpretations of a chemical equation
Pick a household product that has a list of ingredients
with names of covalent compounds or of ions you have met
Equation: 3 H 2 ∙ N 2 → 2 NH 3
in this chapter. Write the brand name of the product and
Molecular ratio: the type of product (for example, Sani-Flush, toilet bowl
cleaner), then list the ingredients as given on the label,
3 molecules H 2 + 1 molecule N 2 → 2 molecules NH 3
writing them one under the other (column 1). Beside each
Mole ratio: name put the formula, if you can figure out what it should
be (column 2). Also, in a third column, put whatever you
3 moles H 2 + 1 mole N 2 → 2 moles NH 3
know or can guess about the function of that substance in
Mass ratio: the product (for example, This is an acid; helps dissolve
mineral deposits).
6.0 g H 2 + 28.0 g N 2 → 34.0 g NH 3

10-17 CHAPTER 10 Chemical Reactions 267