2. Gas Laws
The gas laws deal with how gases behave with respect to pressure,
volume, temperature, and amount.
Gas Laws
The gas laws deal with how gases
behave with respect to pressure,
volume, temperature, and amount.
3. Pressure
Gases are the only state of matter that can be
compressed very tightly or expanded to fill a very
large space. Pressure is force per unit area,
calculated by dividing the force by the area on
which the force acts. The earth's gravity acts on
air molecules to create a force, that of the air
pushing on the earth. This is called atmospheric
pressure.
Pressure
Gases are the only state of matter
that can be compressed very tightly
or expanded to fill a very large space.
Pressure is force per unit area,
calculated by dividing the force by
the area on which the force acts.
The earth's gravity acts on air molecules
to create a force, that of the air pushing
on the earth. This is called atmospheric pressure.
4. • The units of pressure that are used are pascal
(Pa), standard atmosphere (atm), and torr. 1 atm
is the average pressure at sea level. It is
normally used as a standard unit of
pressure. The SI unit though, is the pascal.
101,325 pascals equals 1 atm.
• For laboratory work the atmosphere is very
large. A more convient unit is the torr. 760 torr
equals 1 atm. A torr is the same unit as the
mmHg (millimeter of mercury). It is the pressure
that is needed to raise a tube of mercury 1
millimeter.
5. Boyle's Law:The Pressure -
Volume Law
Robert Boyle (1627-1691)
Boyle's law or the pressure-volume law states that the volume
of a given amount of gas held at constant temperature varies
inversely with the applied pressure when the temperature and
mass are constant.
Robert Boyle (1627-1691)
• Boyle's law or the pressure-volume law states that
the volume of a given amount of gas held
at constant temperature varies inversely
with the applied pressure when the temperature
and mass are constant.
Boyle's Law:The Pressure - Volume Law
6. EXAMPLE:
A sample of gas occupies a volume of 225 ml at a pressure of
720 torr and a temperature of 20°C.Calculate the new pressure
if the volume is increased to 350 ml at constant temperature.
Solution:
P1=720 torr volume increases P2=?
V1=225ml ----------------- V2=350 ml
Pressure decreases
P2=P1 x V1/V2
EXAMPLE:EXAMPLE:
A sample of gas occupies a volume of 225 ml at a pressure
720 torr and a temperature of 20°C.
Calculate the new pressure if the volume
is increased to 350 ml at constant temperature.
Solution:
P1=720 torr P2=?
V1=225ml V2=350 ml
P2=P1 x V1/V2
7. P2=720 torr x 225 ml/350
ml
=463 torr
P2=720 torr x 225 ml/350 ml
=463 torr
8. -
ven amount of gas held at
nal to the Kelvin Temperature.
Charles' Law:The Temperature
-Volume Law
Jacques Charles(1746-1823)
This law states that the volume of a given amount of
gas held at constant pressure is directly proportional
to the Kelvin Temperature.
9. EXAMPLE:
A sample of a gas occupies a volume of 275 ml at 20°C and 1
atm.pressure.Calculate the volume of the gas at 0°C and
1atm.pressure.
Solution:
V1=275 ml V2=?
T1=20+273=293K T2=0+273=273K
V2=275ml x 273K/293K=256ml
A sample of a gas occupies a volume of 275 ml at 20°C and
1 atm.pressure.Calculate the volume of the gas
at 0°C and 1atm.pressure.
Solution:
V1=275 ml V2=?
T1=20+273=293K T2=0+273=273K
V2=275ml x 273K/293K=256ml
EXAMPLE:
10. Gay-Lussac's Law:
The pressure Temperature
Law
Joseph Gay-Lussac(1778-1850)
This law states that the pressure of a given
amount of gas held at constant volume is directly
proportional to the Kelvin Tempetature.
11. Example:
A sample of gas at 25°C has a pressure of 1
atm.Calculate the final pressure in atmospheres if
the temperature us changed to 100°C .
Solution:
P1=1.20atm P2=?
T1=25+273=298K T2=100+273=373K
P1=1.20 atm x 273 K/373K=164atm
12. Avogadro's Law:The Volume
Amount Law
Amedeo Avogadro (1776-1856)
Gives the relationship between volume and amount
when pressure ang temperature are held
constant.Remember amount is measured in
moles.Also,since volume is one of the variables,that
means the container holding the gas is flexible in
some way and can expand or contract.
13. Example #1: 5.00 L of a gas is known
to contain 0.965 mol. If the amount of
gas is increased to 1.80 mol, what
new volume will result (at an
unchanged temperature and
pressure)?
Solution:
V1n2 = V2n1
(5.00 L) (1.80 mol) = (x) (0.965 mol)
14. The Combined Gas Law
The volume of a given amount of gas is
proportional to the ratio of its Kelvin
temperature and its pressure.
15. the volume of a gas filled balloon is 30.0 L
at 40.0L and 1148mm Hg of pressure.What
volume will the balloon have at STP?
P1=1148mmHg P2=1atm=760mmHg
V1=30.0L V2=?
T1=40.0=313K T2=0°=273K
16. The Ideal Gas Law
Ideal Gas Law
An ideal gas is defined as one in which all collisions between atoms or molecules are perfectly
eleastic and in which there are no intermolecular attractive forces. One can visualize it as a
collection of perfectly hard spheres which collide but which otherwise do not interact with each
other. In such a gas, all the internal energy is in the form of kinetic energy and any change in
internal energy is accompanied by a change in temperature.
An ideal gas can be characterized by three state variables: absolute pressure (P), volume (V), and
absolute temperature (T). The relationship between them may be deduced from kinetic theory and
is called the
•n = number of moles
•R = universal gas constant = 8.3145 J/mol K
•N = number of molecules
•k = Boltzmann constant = 1.38066 x 10-23 J/K = 8.617385 x 10-5 eV/K
•k = R/NA
•NA = Avogadro's number = 6.0221 x 1023 /mol
17. 6.2 liters of an ideal gas are contained at 3.0
atm. and 37°C.How many moles of this gas
are present?
Step 1:
Convert °C temp. to K
T=37+273=310
Step2:
n=PV/RT
n=(3.0atm x 6.2 L)/(0.08 L atm/mol K x 310K)
n=0.75mol
