1.1 What is Chemistry?

14.2. Gas Laws http://www.ck12.org

P 2 ×V 2 =k

Therefore,

P 1 ×V 1 =P 2 ×V 2

Example 14.3

A sample of oxygen gas has a volume of 150. mL when its pressure is 0.647 atm. What will the volume of the gas
be at a pressure of 0.987 atm if the temperature remains constant?

Answer

P 1 ×V 1 =P 2 ×V 2

V 1 = 150 .mL,V 2 =?

P 1 = 0 .647 atm,P 2 = 0 .987 atm

V 2 =

P 1 ×V 1

P 2

V 2 =

( 0 .647 atm)( 150. mL)

0 .987 atm

V 2 = 98 .3 mL

Temperature

The thermometer was developed a short time after the barometer made it possible to study pressure in a quantitative
manner. Although crude thermometers had been available for quite some time, Daniel Fahrenheit constructed a more
accurate thermometer in 1724 using mercury in glass. Because the height of the mercury in the thermometer was a
relative measure, certain fixed points needed to be defined. Originally, Fahrenheit defined a 1:1:1 mixture of ice, salt,
and ammonium chloride as 0°F, and the freezing/melting point of ice as 32°F. On this scale, the normal temperature
of the human body is 96°F, and the boiling point of water is 212°C. The modern Fahrenheit scale is defined in terms
of the normal freezing and boiling points of water.

Anders Celsius (1736) devised a slightly different scale, which also had two fixed values based on the freezing and
boiling points of water. Originally, he suggested a value of 0°C for the boiling point and 100°C for the freezing
point. Shortly after his death, the scale was reversed, resulting in the form that is used today. The Celsius scale is the
standard way to measure temperature in most parts of the world.Figure14.6 compares these two different scales.

Absolute Zero

The ideas of absolute zero and absolute temperature were conceived in 1848 by Lord Kelvin. Kelvin had observed
that for every 1°C drop in temperature, a sample of gas contracted by a uniform amount, specifically, 1/273th of
its volume at 0°C. If this data is extrapolated, or projected, to the point where the gas would reach a volume of
zero, we reach a lower limit for possible temperatures. Kelvin interpreted this to mean that -273°C is the lowest
achievable temperature. In contrast to other scales, where the temperature can be below zero, the value of zero
Kelvin represented anabsolute zero.Figure14.7 shows Kelvin’s extrapolation. The Kelvin scale is used for all gas
law calculations.