Chemistry2 nd semester Properties All gases share some physical properties Pressure P Volume V Temperature T Number of moles n These properties combine to describe the behavior of gases using the gas laws ID: 387776
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Slide1
Introduction to Gases
Chemistry—2
nd
semesterSlide2
Properties
All gases share some physical properties:
Pressure (P)
Volume (V)
Temperature (T)
Number of moles (n)
These properties combine to describe the behavior of gases using the “gas laws”Slide3
Pressure
Pressure is the amount of force per given amount of area (P=F/area)
Greater forces exert greater pressure
When the area over which the pressure is exerted is
decreased
, the pressure is
increasedSlide4
Pressure Cont.
Pressure is the result of collisions of gas molecules and the sides of a containerSlide5
Applications
Why is there more pressure on you the deeper you move in a body of water?
Why is it harder to breathe when you’re up in a mountain?Slide6
Applications
Why is there more pressure on you the deeper you move in a body of water?
There is more water pushing down on you. Greater force means greater pressure
Why is it harder to breathe when you’re up in a mountain?
The air is “thinner” which means there is less atmospheric pressure because there is less air pushing down on youSlide7
Atmospheric Pressure
The pressure exerted by the atmosphere on the earth
Decreases as you move up
About 15 psi (pounds per square inch) at sea levelSlide8
Standard Pressure
“normal” atmospheric pressure at sea level
Standard Pressure:
1.00
atm
(atmospheres)
101.3
kPa
(kilopascals)
760 mmHg (millimeters of mercury)
760
torrSlide9
Standard temperature
Absolute temperature is measured in Kelvin (K)
0 K is absolute zero
K = °C + 273
°C = K – 273
Standard temperature: 273 KSlide10
Ways to measure pressure
BarometerSlide11
Ways to measure pressure
ManometerSlide12
Kinetic Theory of Gases
A set of ideas (5 points) used to describe and explain the behavior of gases
Any gas that behaves exactly in this manner is called an “ideal gas”
There are not any “ideal gases” in real life. Real gases behave much like “ideal” gases unless they are under high pressure and temp.Slide13
Point One
Gases are composed of tiny particles called molecules
Molecules are so far apart that gases are mostly empty space
Because of this, gases can be easily compressed and mixedSlide14Slide15
Point Two
Gas molecules posses kinetic energy (KE=1/2mv
2
)
Gas molecules are in
constant, random, straight line
motionSlide16Slide17
Point Three
Collisions between gas molecules and each other or the container are
elastic
No kinetic energy is changed into another form of energy (like heat)
The pressure of an enclosed gas will NOT change unless its temperature or volume changesSlide18
Point Four
Molecules of a gas are not attracted to or repulsed by each other
They move independently of each otherSlide19
Point Five
Individual molecules of a gas are moving at different speeds because they have different kinetic energies
The average kinetic energy (speed) is directly proportional to the temperature of a gasSlide20
Dalton’s Law of Partial Pressure
The total pressure of a mixture of gases is the sum of the
partial pressures
of the
individual
gases
P
T
= P
1
+ P
2
+ P
3
+ .......Slide21Slide22
Effusion
Effusion is the movement of gas molecules through an extremely tiny opening into a region of lower pressure
helium escaping a balloon
air leaking from a tireSlide23
Diffusion
Diffusion is the tendency of molecules to move toward areas of lower concentration until the concentration is uniform throughout the system
mixing of gasesSlide24
Graham’s Law of Effusion
Molecules
of lower molar mass diffuse and effuse faster.