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Introduction to Gases. Chemistry—2 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”. Pressure.

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introduction to gases

Introduction to Gases

Chemistry—2nd semester

properties
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”
pressure
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 increased
pressure cont
Pressure Cont.
  • Pressure is the result of collisions of gas molecules and the sides of a container
applications
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?
applications1
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 you
atmospheric pressure
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 level
standard pressure
Standard Pressure
  • “normal” atmospheric pressure at sea level
  • Standard Pressure:
    • 1.00 atm (atmospheres)
    • 101.3 kPa (kilopascals)
    • 760 mmHg (millimeters of mercury)
    • 760 torr
standard temperature
Standard temperature
  • Absolute temperature is measured in Kelvin (K)
  • 0 K is absolute zero
  • K = °C + 273
  • °C = K – 273
  • Standard temperature: 273 K
kinetic theory of gases
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.
point one
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 mixed
point two
Point Two
  • Gas molecules posses kinetic energy (KE=1/2mv2)
  • Gas molecules are in constant, random, straight linemotion
point three
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 changes
point four
Point Four
  • Molecules of a gas are not attracted to or repulsed by each other
  • They move independently of each other
point five
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 gas
dalton s law of partial pressure
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
  • PT = P1 + P2 + P3 + .......
effusion
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 tire
diffusion
Diffusion
  • Diffusion is the tendency of molecules to move toward areas of lower concentration until the concentration is uniform throughout the system
    • mixing of gases
graham s law of effusion
Graham’s Law of Effusion
  • Molecules of lower molar mass diffuse and effuse faster.