Introduction to Gases Chemistry2 nd semester. Properties All gases share some physical properties: Pressure (P) Volume (V) Temperature (T) Number of moles.

Introduction to GasesChemistry—2nd semester

PropertiesAll 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”

PressurePressure 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

ApplicationsWhy 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?

ApplicationsWhy 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 PressureThe pressure exerted by the

atmosphere on the earthDecreases as you move upAbout 15 psi (pounds per square

inch) at sea level

Standard Pressure“normal” atmospheric pressure

at sea levelStandard Pressure:

◦1.00 atm (atmospheres)◦101.3 kPa (kilopascals)◦760 mmHg (millimeters of mercury)◦760 torr

Standard temperatureAbsolute temperature is

measured in Kelvin (K)0 K is absolute zero

K = °C + 273°C = K – 273

Standard temperature: 273 K

Ways to measure pressureBarometer

Ways to measure pressureManometer

Kinetic Theory of GasesA 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 OneGases are composed of tiny

particles called moleculesMolecules are so far apart that

gases are mostly empty spaceBecause of this, gases can be

easily compressed and mixed

Point TwoGas molecules posses kinetic

energy (KE=1/2mv2)Gas molecules are in constant,

random, straight line motion

Point ThreeCollisions 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 FourMolecules of a gas are not

attracted to or repulsed by each other

They move independently of each other

Point FiveIndividual 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.