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Unformatted text preview: ures, we have volume. Volume is an effect of the third dimension, which is
where most of us exist, although there may be those who seem to be from dimensions other than
our own. Anyway, let’s start out with a length, say 1 cm. If we attach another length to the end
of the first one, also 1 cm, we have defined a box, which has area. The area is the two sides
multiplied together, or, 1 cm2 . To add a third dimension, we can place a 1 cm line connected at
the same point where the first two lines are connected and at a right angle to each of them. The
only way this is possible is to place it perpendicular to the plane defined by the first two lines,
thereby defining a box. The volume of the box will be the length of all three sides multiplied
together, or 1 cm3 . This volume is one c ubic centimeter, or 1 cc. It is also, by definition, 1 mL.
Thus, 1 cm3 = 1 cc = 1 mL. The mL is the connection to liters, L, which is the metric unit used
Pressure, on the other hand, is a force per unit area. Force is mass (a measure of the
quantity of matter) times acceleration, F=ma. The most familiar force in this country is the
pound, lb. Weight is a force. The acceleration is acceleration due to gravity, which is smaller on
the moon. The amount of matter we would have on the moon, m, would be constant and thus,
our mass would be constant, but because the acceleration constant due to gravity, a, would be
smaller on the moon than it is on the earth, our weight would be less on the moon than here on
earth. So, if we take a weight and divide that weight by an area, we have force. For instance,
suppose there is a person that weighs 180 lb with feet that have a surface area (in shoes) of about
99 in2 . Then the pressure that person is exerting on the earth as he or she is standing still is 180
lb/99 in2 = 1.82 lb/in2 = 1.82 psi. (“psi” stands for “pounds per square inch”.)
Dakota State University Page 126 of 232 Experiment 10: Gas Laws General Chemistry I and II Lab Manual Boyle’s law relates gas volume to pressure. Boyle carefully measured how the volume of
a gas changes as he varied the pressure on that gas. He discovered that for a system with a fixed
amount of gas (n) and temperature (T), a plot of volume versus pressure gave a straight line with
a negative slope. A more common way to state this would be to say that as pressur e increases,
volume decreases. We say that for constant n and T, volume is inversely proportional to
Vα 1/P |n,T
VP = k |n,T The vertical line above with the subscript “n,T” is a mathematical symbolism used to remind us
that this is true only if the number of moles of the gas n and the temperature T remain constant.
A proportionality can be converted into an equation with the introduction of some constant, in
V = k/P |n,T
our case k, even if we do not know the value of this constant. Thus,
or, since k must be constant, V1 P1 = V2 P2
for any two states 1 and 2 (that is, for any initial state 1 to any final state 2 where we vary either
pressure or volume.
Charles’ decided that he was rather more interested in the rel...
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