Introduction to Gases

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# Introduction to Gases - PowerPoint PPT Presentation

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

Chemistry—2nd 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
• 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 is the result of collisions of gas molecules and the sides of a container
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?
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
• 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
• “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
• 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
• 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
• 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
• Gas molecules posses kinetic energy (KE=1/2mv2)
• Gas molecules are in constant, random, straight linemotion
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
• Molecules of a gas are not attracted to or repulsed by each other
• They move independently of each other
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
• 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 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 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
• Molecules of lower molar mass diffuse and effuse faster.