Chapter 10 Chapter 10 Physical Characteristics Physical Characteristics of Gases of Gases
Dec 27, 2015
Kinetic Molecular Kinetic Molecular TheoryTheory
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 Kelvin
temperature of a gas.
Ideal Ideal GasesGases
Ideal gases are imaginary gases that perfectlyfit all of the assumptions of the kinetic moleculartheory.
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 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.
The Nature of GasesThe Nature of Gases
Gases expand to fill their containersGases are fluid – they flowGases have low density
1/1000 the density of the equivalent liquid or solid
Gases are compressibleGases effuse and diffuse
Diffusion: describes the mixing of gases. The rate of diffusion is the rate of gas mixing.
DiffusionDiffusion
PressurePressure
Is caused by the collisions of molecules with the walls of a containeris equal to force/unit areaSI units = Newton/meter2 = 1 Pascal (Pa)1 standard atmosphere = 101,325 Pa1 standard atmosphere = 1 atm =
760 mm Hg = 760 torr
Measuring Measuring PressurePressure
The first device for measuring atmosphericpressure was developed by Evangelista Torricelli during the 17th century.The device was called a “barometer”
Baro = weight Meter = measure
An Early An Early BarometerBarometer
The normal pressure due to the atmosphere at sea level can support a column of mercury that is 760 mm high.
Standard Temperature and Standard Temperature and PressurePressure
“STP”“STP”
P = 1 atmosphere, 760 torr T = C, 273 Kelvins The molar volume of an ideal gas is 22.42 liters at STP
Robert BoyleRobert Boyle((1627-1691)1627-1691)
o Boyle was born into an aristocratic Irish family
o Became interested in medicine and the new science of Galileo and studied chemistry.
o A founder and an influential fellow of the Royal Society of London
o Wrote prolifically on science, philosophy, and theology.
Boyle’s LawBoyle’s Law**
Pressure Volume = Constant P1V1 = P2V2 (T = constant)
Pressure is inversely proportional to volumewhen temperature is held constant.
Why Don’t I Get a Constant Value for PV = k?
1. Air is not made
of ideal gases2. Real gases deviate from ideal behaviorat high pressure
Jaques Charles (1746-1823Jaques Charles (1746-1823)
French Physicist Conducted the first
scientific balloon flight in 1783
Charles’s LawCharles’s Law
The volume of a gas is directly proportional to temperature, and extrapolates to zero at zero Kelvin.
(P = constant)
VT
VT
P1
1
2
2 ( constant)
Converting Celsius to KelvinConverting Celsius to Kelvin
Gas law problems involving temperature require that the temperature be in KELVINS!
Kelvins = C + 273
°C = Kelvins - 273
Gay Lussac’s LawGay Lussac’s Law
The pressure and temperature of a gas aredirectly related, provided that the volume remains constant.
2
2
1
1
T
P
T
P
Joseph Louis Gay-LussacJoseph Louis Gay-Lussac1778 - 18501778 - 1850
French chemist and physicist Known for his studies on the physical properties of gases. In 1804 he made balloon ascensions to study magnetic forces and to observe the composition and temperature of the air at different altitudes.
The Combined Gas LawThe Combined Gas Law
The combined gas law expresses the relationship between pressure, volume and temperature of a fixed amount of gas.
2
22
1
11
T
VP
T
VP