Section 9.2

Definition: a measure of the average kinetic energy of a substance’s particles

Generally measured in o C The Kelvin temperature scale (K) is based on

absolute temperature absolute zero (point where gas molecules have

no motion) is 0 K and/or -273oC Kelvin temperatures must be used in many gas

law equations in which temperature enters directly into the calculations. 

The Celsius and Kelvin scale are related unit for unit. One degree unit on the Celsius scale is equivalent to one degree unit on the Kelvin scale. The only difference between these two scales is the zero point. 

so, this means that 0 K equals -273 oC and 0oC equals 273 K. Thermometers are never marked in the Kelvin scale.

to convert temperature units, use the following equations. 

TK =  tc  +  273 

or      tc  =  TK  -  273

Cold Saunas are available at high end resorts. Instead of heating the sauna and causing the people inside to sweat, a cold sauna is cooled down to -110 ° C. What would the temperature be in Kelvin?

TK =  tc  +  273  TK =  -110  +  273  TK =  163 K

Helium has the lowest boiling point of any gas. It boils at 4 K. What is this in oC?

tc = TK -  273  tc =  4K -  273  tc =  -269 oC

Section 9.2

The direct relationship between the volume and temperature of a gas is known as Charles Law. According to this law,

as the temperature of a gas increases, the volume increases proportionally, provided that the pressure and the amount of gas remains the same.

the graph below shows this relationship. Charles’s Law can be written as

V1= V2

  T1 T2

The volume of a sample of gas is 23.2 cm3 at 20oC. If the pressure remains unchanged, what is its volume at 80oC?

G V1 = 23.2 cm3 

T1 = 20oC = 293 K

T2 = 80oC = 353K

S V2 = (23.2 cm3 x 353 K)

293 K

= 27.95 cm3

R V2 = ? P Therefore, when the temperature increased by 60 K, it increased the volume

from 23.2 cm3 to 27.95 cm3

A V1= V2

T1 T2

V2 = V1T2

T1

Compressed oxygen is widely used in hospitals and retirement homes. To make it easier to transport, the oxygen is cooled. How many degrees Celsius would the gas be if 200 L at 23 degrees Celsius is compressed to 40 L?

G V1 = 200 L

T1 = 23oC = 296 K

V2 = 40 L

S T2 = (40 L x 296 K )

200 L = 59. 2 K = -213. 8 oC

R T2 = ? P Therefore, when the gas is compressed for transport it is cooled to -213. 8 oC.

A V1= V2

T1 T2

T2 = V2T1 / V1

Read pg. 429 – 434Questions:

page 432 # 13-14page 434 # 16-19, 21Worksheet: Charles’ Law