Gases Properties Kinetic Molecular Theory Variables The Atmosphere Gas Laws.
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Transcript of Gases Properties Kinetic Molecular Theory Variables The Atmosphere Gas Laws.
Properties of a Gas No definite shape or volume
Gases expand to fill any container
Thus they take the shape of the container, as well as the volume!
Low Density Most of the volume of a gas is
empty space-since the gas particles want to be as far from all like particles as possible
As a result, gases are compressible
The Atmosphere
Composed of a mixture of gases
-Approx. 80% N2 and 20% O2
Provides conditions for life, protects from UV radiation, traps heat
Please read about the Greenhouse Effect and the Ozone Layer in your text books…you will be responsible for that information...
The Kinetic Molecular Theory
Explains the behavior of gases at the molecular level
Based on assumptions about a theoretical gas referred to as the Ideal Gas.
The Kinetic Molecular Theory1) Volume of gas particles is
essentially zero (Point Masses)
2) Particles are in constant, random motion
3) No attractive forces betw. particles and collisions are perfectly elastic No energy is lost by the
particles during collisions
The Kinetic Molecular Theory
4) The temperature of a gas is directly proportional to the average kinetic energy associated with the particles, thus the higher the temperature, the faster the particles are moving... K.E. = 1/2 mv2
Ideal vs. Real Gas
Ideal Gas Has mass but
no volume Has no
attractive forces between molecules
Real Gas Molecules do
have volume Molecules
exert an attractive force on each other when very close.
Four variables that describe a gas...
1) Temperature - the measure of the avg. kinetic energy
gases at the same temp. must have the same avg. kinetic energy
Must be in Kelvin!
TK = TC + 273
Four variables that describe a gas...
2) Volume - The amount of space occupied by the particles, measured in
liters, mL, cm3, m3, etc.
Four variables that describe a gas...
3) Pressure - The force exerted by the gas per unit of area
In gases - meas. of total force exerted by the particles colliding w/ the walls of their container. - proportional to the number of
collisions• -Incr. temp, incr. press.• - Incr. # of particles, incr. press.
usually measured in: atmospheres (atm), kPa (kilo-pascals), N/m2
Pascal - SI unit of pressure• = to 1 N/m2 • very small press. - usually use kilopascals
Four variables that describe a gas...
4) Number of particlesEqual volumes of gases under the same conditions have equal numbers of particles...
Avogadro’s PrincipleThe volume of a gas at a given
temperature and pressure is directly proportional to the number of moles of that gas
ie equal volumes of gases under the same conditions contain the same number of particles.
Molar Volume is the volume of 1 mole of any gas at STP
Standard ConditionsSTP
Standard Temperature is 273 K
Standard Pressure is…
1.0000 atm
101.325 kPa
760.0 mm Hg
760.0 torr
Note: you can use any pressure units but you can only use Kelvin temperature units!
The Gas Laws
Boyle’s Law
- the volume of a gas at constant temp. is inversely proportional to the pressure
P1 V1 = P2 V2
Read Ch. 12 Section 2
The Gas Laws
Charles’ Law - the volume of a gas at constant press. is directly proportional to the absolute (Kelvin) temp.
V1 / T1 = V2 / T2
The Gas Laws
Combined Gas Law - Combines Boyle’s & Charles’ Law
P1V1 / T1 = P2V2 / T2
Read Ch. 12 Section 2