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Introduction to Gases

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

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  1. Introduction to Gases Chemistry—2nd semester

  2. 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”

  3. 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

  4. Pressure Cont. • Pressure is the result of collisions of gas molecules and the sides of a container

  5. 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?

  6. 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

  7. 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

  8. 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

  9. Standard temperature • Absolute temperature is measured in Kelvin (K) • 0 K is absolute zero • K = °C + 273 • °C = K – 273 • Standard temperature: 273 K

  10. Ways to measure pressure • Barometer

  11. Ways to measure pressure • Manometer

  12. 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.

  13. 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

  14. Point Two • Gas molecules posses kinetic energy (KE=1/2mv2) • Gas molecules are in constant, random, straight linemotion

  15. 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

  16. Point Four • Molecules of a gas are not attracted to or repulsed by each other • They move independently of each other

  17. 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

  18. 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 + .......

  19. 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

  20. 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

  21. Graham’s Law of Effusion • Molecules of lower molar mass diffuse and effuse faster.

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