Physical Chemistry Third Edition

8 1 The Behavior of Gases and Liquids

fuel before reaching its destination. Fortunately, the pilot was able to glide to a former

military air field and make a “deadstick” landing on an unused runway. Some people

who were having a picnic on the runway were fortunately able to get out of the way in

time. There was even a movie made about this incident.

The official set of units that physicists and chemists use is theInternational System

of Units,orSI units.The letters SI stand forSysteme Internationale, the French name

for the set of units. In this system there are sevenbase units. The unit of length is the

meter(m). The unit of mass is thekilogram(kg). The unit of time is thesecond(s). The

unit of temperature is thekelvin(K). The unit of electric current is theampere(A).

The unit of luminous intensity is thecandela(cd). The unit for the amount of a

substance is themole(mol). The SI units are calledMKS(meter-kilogram-second)

units. Prior to 1961, most chemists and some physicists usedcgs(centimeter-gram-

second) units, but we now use SI units to avoid confusion.

The newton is named for Sir Isaac
Newton, 1642–1727, the great English
mathematician and physicist who
invented classical mechanics and who
was one of the inventors of calculus.

The pascal is named for Blaise Pascal,
1623–1662, a famous French
philosopher, theologian, and
mathematician.

In addition to the seven base units, there are a number ofderived units. Thenewton

(N) is the SI unit of force:

1N1kgms−^2 (definition) (1.1-5)

Thepascal(Pa) is the SI unit of pressure (force per unit area):

1Pa1Nm−^2 1kgm−^1 s−^2 (definition) (1.1-6)

We have enclosed these defining equations in boxes, and will enclose the most important

equations in boxes throughout the rest of the book.

A force exerted through a distance is equivalent to an amount of work, which is a

form of energy. The SI unit of energy is thejoule(J):

1J1Nm1kgm^2 s−^2 (definition) (1.1-7)

The joule is named for James Prescott
Joule, 1818–1889, a great English
physicist who pioneered in the
thermodynamic study of work, heat,
and energy in a laboratory that he
constructed in his family’s brewery. Multiples and submultiples ofSIunits are indicated by prefixes, such as “milli” for
1/1000, “centi” for 1/100, “deci” for 1/10, “kilo” for 1000, and so on. These prefixes are
listed inside the cover of this book. We do not use double prefixes such as millikilogram
for the gram or microkilogram for the milligram.
We will also use some non-SI units. Thecalorie(cal), which was originally defined
as the amount of heat required to raise the temperature of 1 gram of water by 1◦C, is
now defined by:

1 cal4.184 J (exactly, by definition) (1.1-8)

We will use several non-SI units of pressure; theatmosphere(atm), thetorr, and thebar.

1 atm101325 Pa (exactly, by definition) (1.1-9)

760 torr1 atm (exactly, by definition) (1.1-10)

1 bar100000 Pa (exactly, by definition) (1.1-11)

The angstrom (Å, equal to 10−^10 mor10−^8 cm) has been a favorite unit of length

among chemists, because it is roughly equal to a typical atomic radius. Picometers are

nearly as convenient, with 100 pm equal to 1 Å. Chemists are also reluctant to abandon

theliter(L), which is the same as 0.001 m^3 or 1 dm^3 (cubic decimeter).