Transcript The Empirical Gas Laws

Lesson 3
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In SI Metric the temperature scale is defined
as Kelvin temperature scale.
The degree unit is the Kelvin (K). The symbol
for the unit is K, not o K.
Kelvin temperatures must be used in many
gas law equations in which temperature
enters directly into the calculations.
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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.
The zero point on the Celsius scale was
defined as the freezing point of water, which
means that there are higher and lower
temperatures around it.
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The zero point on the Kelvin
scale - called absolute
zero – it corresponds to the
lowest temperature that is
possible. It is 273.15 units
lower than the zero point on
the Celsius scale.
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So this means that 0 K equals -273.15 oC and
0oC equals 273.15 K. Thermometers are
never marked in the Kelvin scale.
If we need degrees in Kelvin the following
relationships are to be used.
TK = tc + 273.15
or
tc = TK - 273.15
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Cold Saunas are available a 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 + 273.15
TK = -110 + 273.15
TK = 163.15 K
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Liquid nitrogen (sometimes abbreviated LOX)
is used in liquid-fuel rockets. Its boiling point
is -183oC. What is this temperature in
Kelvin’s?
A substance is heated from 300 K to 315 K.
What is the change in temperature expressed
in °C.
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Perform the following conversions
a)24°C to K
a)50 K to °C
a)30 °C to K
a)215. 15 K to °C
a)-37.89 °C to K
a)333. 67 K to °C.
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A clinical thermometer registers a patient's
temperature to be 37.13oC. What is this in
Kelvin’s?
The coldest permanently inhabited place on
earth is the Siberian village of Oymyakon in
Russia. In 1964 the temperature reached a
shivering -71.11oC. What is this temperature
in Kelvin’s?
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Helium has the lowest boiling point of any
liquid. It boils at 4 K. What is this in oC?
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The direct relationship between the volume of
a gas and the temperature of the gas (on the
Kelvin temperature scale) 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.
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However, as the graph above shows, the
volume extrapolates to zero at a temperature
of -273.15oC. If this temperature were taken
as the zero of a temperature scale then all
negative temperatures could be eliminated.
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Such a temperature scale is now the
fundamental scale of temperature in the SI. It
is called the absolute scale, the
thermodynamic scale, and the Kelvin scale.
Temperature on the Kelvin scale, and only on
the Kelvin scale, is symbolized by T.
Charles’s Law can be written as
V 1 T 2= V 2 T 1
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The volume of a sample of gas is 23.2 cm3 at
20oC. If the gas is ideal and the pressure
remains unchanged what is its volume at
80oC?
G
V1 = 23.2 cm3
T1 = 20oC = 293.15 K
T2 = 80oC = 353.15K
S
V2 = (23.2 cm3 x 353.15K)
293.15 K
= 27.95 cm3
R
V2 = ?
P
A
V1T2= V2T1
Therefore, when the
temperature increased by 60
K it increased the volume
from 23.2 cm3 to 27.95 cm3
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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’s at 23 degrees Celsius is
compressed to 40 L?
G
V1 = 200 L
T1 = 23oC = 296.15 K
V2 = 40 L
S
T2 = (40 L x 296.15 K )
200 L
= 59. 23 K = -213. 9 oC
R
T2 = ?
P
A
V1T2= V2T1
T2 = V2T1 / V1
Therefore, when the gas
is compressed for
transport it is cooled to 213. 9 oC.
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Questions:
page 432 # 13-14
page 434 # 16-19.
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Temperature and pressure law next
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When a gas is heated the pressure also
increases, if we assume the volume and the
amount of gas remains the same, the
quotient of the two variables (p/T) has a
constant value (k).
Because it remains the same it allows us to
compare different sets of temperatures and
pressures.
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This is known as the pressure and
temperature law or the Gay-Lussac’s Law.
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An aerosol can of paint contains a pressure of
138 kPa at 20 °C. The can is left in a parked
car and is heated to 50 ° C. What it the final
pressure in the can?
G
R
A
P1 = 138 kPa
T1 = 20oC = 293.15 K
T2 = 50oC = 323.15K
P2 = ?
S
P
= 152 kPa
Therefore, when the paint
can is heated an additional
30 ° C the pressure increases
to 152 kPa.
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page 432 # 13-14
page 434 # 16-19.
Page 435 # 22-25