Unit 5: Gasesand Gas Laws : Unit 5: Gasesand Gas Laws
Kinetic Molecular Theory : Kinetic Molecular Theory Particles of matter are ALWAYS in motion
Volume of individual particles is zero.
Collisions of particles with container walls cause pressure exerted by gas.
Particles exert no forces on each other.
Average kinetic energy µ Kelvin temperature of a gas.
The Meaning of Temperature : The Meaning of Temperature Kelvin temperature is an index of the random motions of gas particles (higher T means greater motion.)
Kinetic Energy of Gas Particles : Kinetic Energy of Gas Particles At the same conditions of temperature, all gases have the same average kinetic energy. m = mass v = velocity
Measuring Pressure : Measuring Pressure The first device for measuring atmospheric
pressure was developed by Evangelista Torricelli
during the 17th century. The device was called a “barometer” Baro = weight
Meter = measure
An Early Barometer : An Early Barometer The normal pressure due to
the atmosphere at sea level
can support a column of
mercury that is 760 mm high.
The Aneroid Barometer : The Aneroid Barometer
Pressure : Pressure Is caused by the collisions of molecules with the walls of a container
is equal to force/unit area
SI units = Newton/meter2 = 1 Pascal (Pa)
1 standard atmosphere = 101.3 kPa
1 standard atmosphere = 1 atm =
760 mm Hg = 760 torr
Units of Pressure : Units of Pressure
The Nature of Gases : The Nature of Gases Gases expand to fill their containers
Gases are fluid – they flow
Gases have low density
1/1000 the density of the equivalent liquid or solid
Gases are compressible
Gases effuse and diffuse
Standard Temperature and Pressure“STP” : Standard Temperature and Pressure“STP” P = 1 atmosphere, 760 torr, 101.3 kPa
T = 0°C, 273 Kelvins
The molar volume of an ideal gas is 22.42 liters at STP
Boyle’s Law : Boyle’s Law Pressure is inversely proportional to volume
when temperature is held constant.
A Graph of Boyle’s Law : A Graph of Boyle’s Law
Converting Celsius to Kelvin : Converting Celsius to Kelvin Gas law problems involving temperature require that the temperature be in KELVINS! Kelvins = C + 273 °C = Kelvins - 273
Charles’s Law : Charles’s Law The volume of a gas is directly proportional to temperature, and extrapolates to zero at zero Kelvin.
(P = constant) Temperature MUST be in KELVINS!
A Graph of Charles’ Law : A Graph of Charles’ Law
Gay Lussac’s Law : Gay Lussac’s Law The pressure and temperature of a gas are
directly related, provided that the volume
remains constant. Temperature MUST be in KELVINS!
A Graph of Gay-Lussac’s Law : A Graph of Gay-Lussac’s Law
The Combined Gas Law : The Combined Gas Law The combined gas law expresses the relationship between pressure, volume and temperature of a fixed amount of gas. Boyle’s law, Gay-Lussac’s law, and Charles’ law are all derived from this by holding a variable constant.
Standard Molar Volume : Standard Molar Volume Equal volumes of all gases at the same temperature and pressure contain the same number of molecules.
- Amedeo Avogadro
Ideal Gas Law : Ideal Gas Law PV = nRT
P = pressure in atm
V = volume in liters
n = moles
R = proportionality constant
= 0.08206 L atm/ mol·K
T = temperature in Kelvins Holds closely at P < 1 atm
Gas Density : Gas Density … so at STP…
Density and the Ideal Gas Law : Density and the Ideal Gas Law Combining the formula for density with the Ideal
Gas law, substituting and rearranging algebraically: M = Molar Mass
P = Pressure
R = Gas Constant
T = Temperature in Kelvins
Ideal Gases : Ideal Gases Ideal gases are imaginary gases that perfectly fit all of the assumptions of the kinetic molecular theory. Gases consist of tiny particles that are far apart
relative to their size. Collisions between gas particles and between
particles and the walls of the container are
elastic collisions No kinetic energy is lost in elastic
collisions
Ideal Gases (continued) : Ideal Gases (continued) Gas particles are in constant, rapid motion. They
therefore possess kinetic energy, the energy of
motion There are no forces of attraction between gas
particles The average kinetic energy of gas particles
depends on temperature, not on the identity
of the particle.
Real Gases Do Not Behave Ideally : Real Gases Do Not Behave Ideally Real gases DO experience inter-molecular attractions Real gases DO have volume Real gases DO NOT have elastic collisions
Deviations from Ideal Behavior : Deviations from Ideal Behavior
Dalton’s Law of Partial Pressures : Dalton’s Law of Partial Pressures For a mixture of gases in a container,
PTotal = P1 + P2 + P3 + . . . This is particularly useful in calculating the pressure of gases collected over water.
Diffusion : Diffusion: describes the mixing of gases. The rate of diffusion is the rate of gas mixing. Diffusion
Effusion : Effusion Effusion: describes the passage of gas into an evacuated chamber.
Graham’s LawRates of Effusion and Diffusion : Effusion: Diffusion: Graham’s LawRates of Effusion and Diffusion