Geoscience Reference
In-Depth Information
TABLE 15.1
Comparison of Temperature Scales
Temperature Scale
Celsius (°C)
Kelvin (K)
Fahrenheit (°F)
Rankine (°R)
Boiling point of water
+ 100
+ 373.15
+ 212
+671.67
↑
100 equal
divisions
↓
↑
100 equal
divisions
↓
↑
180 equal
divisions
↓
↑
180 equal
divisions
↓
Freezing point of water
0
273.15
+32
+491.67
Absolute zero
-273.15
0
-459.67
0
Note:
Units of temperature that we will run into include degrees Celsius and Kelvin (equal
to 273 plus degrees Celsius). The degree symbol (°) is not used for the Kelvin tem-
perature scale.
On the Celsius scale, the freezing point of water is assigned a value of 0 and the boiling point a
value of 100; the distance between these two points is divided into 100 equal increments, with each
increment labeled in Celsius degree (Table 15.1). On the Kelvin scale, the freezing point of water is
assigned a value of 273.15 K and the boiling point a value of 373.15; the distance between these two
points is divided into 100 equal increments, and each increment is labeled as a Kelvin (Table 15.1).
On the Fahrenheit scale, the freezing point of water is assigned a value of 32 and the boiling point a
value of 212; the distance between these two points is divided into 180 equal increments, and each
increment is labeled as a Fahrenheit degree (Table 15.1).
15.5.2.1.1 Boyle's L aw
Circa 1662, Robert Boyle stated what has come to be known as Boyle's law: The volume of any
definite quantity of gas at constant temperature varies inversely as the pressure on the gas:
P
1
×
V
1
=
P
2
×
V
2
(15.4)
In this equation,
P
1
is the initial pressure of the gas, and
V
1
is the initial volume of the gas.
P
2
is the
final pressure of the gas, and
V
2
is the final volume of the gas. If we know the initial pressure and
volume of a gas and know what the final pressure will be, we can predict what the volume will be
after we put the pressure on it.
■
EXAMPLE 15.1
Problem:
If we have 4 L of methane gas at a pressure of 1.0 atm, what will be the pressure of the
gas if we compress it so is has a volume of 2.5 L?
Solution:
1.0 atm × 4 L =
x
atm × 2.5 L
x
= 1.6 atm
15.5.2.1.2 Charles' Law
Charles observed that hydrogen (H
2
), carbon dioxide (CO
2
), oxygen (O
2
), and air expanded by an
equal amount when heated from 0°C to 80°C at a constant pressure:
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