The Foundations of Chemistry

Zn88nZn^2  2 e (oxidation, anode)

Cu^2  2 e88nCu (reduction, cathode)

Cu^2 Zn88nCuZn^2  (overall cell reaction)

Electrons are released at the anode and consumed at the cathode. They therefore flow

through the wire from anode to cathode, as in all electrochemical cells. In all voltaiccells

the electrons flow spontaneously from the negative electrode to the positive electrode. So,

in contrast with electrolytic cells, the anode is negative and the cathode is positive. To

maintain electroneutrality and complete the circuit, two Clions from the salt bridge

migrate into the anode solution for every Zn^2 ion formed. Two Kions migrate into

860 CHAPTER 21: Electrochemistry

CC Our Daily Lives

HEMISTRY IN USE

A Spectacular View of One Mole of

Electrons

Early in our study of chemistry, we saw that atoms are made

up of protons, neutrons, and electrons. We also discussed the

incredibly large size of Avogadro’s number, 6.022 1023.

Although individual atoms and molecules are invisible to the

naked eye, one mole of atoms or molecules is easily detected.

Because subatomic particles are even smaller than atoms and

also invisible, you might never expect to see individual elec-

trons. Let’s consider the possibility, however, of seeing a

faraday of charge. A faraday of charge contains Avogadro’s

number of electrons. Would this collection of 6.022 1023

electrons be visible? If so, what might it look like? It would

look quite spectacular!

Throughout the 1980s, scientists carefully studied data

collected during 5 million lightning flashes along the eastern

United States. The data were collected by 36 instruments

that were collectively known as the National Lightning

Detection Network. The investigating scientists found that

the electrical currents in lightning flashes over northern

Florida measured about 45,000 amps, about double the

25,000-amp currents in lightning flashes over the New Eng-

land states. This study showed that the amount of current

flowing during lightning flashes was inversely proportional

to the latitude (distance from the equator) of the storm.

One coulomb is the amount of charge that passes a point

when a one-ampere current flows for one second (1 cou-

lomb1 amperesecond). Thus, a current of 96,500 amps

flowing for one second contains Avogadro’s number of elec-

trons, or one faraday of charge.

Measurements taken in northern Florida show that a typ-

ical two-second lightning strike over that section of the

country would transfer approximately Avogadro’s number of

electrons between the clouds and the earth. So, for those liv-

ing in northern Florida, a spectacular mental view of one

mole of electrons can be obtained by visualizing a two-

second lightning strike. Keep in mind that the average light-

ning strike lasts only a small fraction of a second, and that

we can only have a mental view of a two-second lightning

strike by extrapolation of what is seen in nature. Because New

England lightning strikes produce only about half the cur-

rent of lightning strikes over northern Florida, people in New

England must try to imagine a four-second lightning strike.

Ronald DeLorenzo

Middle Georgia College

Compare the/, anode–cathode,
and oxidation–reduction labels and the
directions of electron flow in Figures
21-2a and 21-6.