chapter 12 physical characteristics of gases. kinetic molecular theory particles of matter are...
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Chapter 12Chapter 12Physical Physical
Characteristics of Characteristics of GasesGases
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.
The Meaning of TemperatureThe Meaning of Temperature
Kelvin temperature is an index of the random motions of gas particles (higher Temp means greater motion & greater ENERGY.)
(KE)32avg RT
Kinetic Energy of Gas Kinetic Energy of Gas ParticlesParticles
At the same conditions of temperature, all gases have the same average kinetic energy.
2
2
1mvKE
The Nature of GasesThe 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
Diffusion: describes the mixing of gases. The rate of diffusion is the rate of gas mixing.
DiffusionDiffusion
EffusionEffusionEffusion: describes the movement of gas from an area of HIGHER gas concentration to an area of LOWER gas concentration.
PressurePressure 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) Atmospheres (atm) is the unit most
commonly used in Chemistry. 1 atm = 760 mm Hg
= 760 torr = 101,325 Pa
= 101.325 kPa
Ideal Gases vs Ideal Gases vs Real Real GasesGases
Ideal gases are imaginary gases that perfectly fit all of the assumptions of the kinetic molecular theory.
Ideal: 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
Real: Same!
Real: No perfectly elastic collisions. Some
energy is lost or gained in every collision.
Ideal vs. Ideal vs. RealReal Gases Gases (continued)
Gas particles are in constant, rapid, random motion. They therefore possess kinetic energy, the energy of motion
There are no forces of attraction between gas particles
Real: Yes EXCEPT when gas gets VERY cold. At Absolute zero there is no molecular motion. Absolute zero = O Kelvein, - 273 oC, or -459 oF
Real: NO! All gases are made of protons and
electrons which attract each other!
Polar Gases (H2O & NH3 can have strong attractions between molecules.
The kinetic energy of gas particles depends on temperature, not on the identity of the particle.
Real: NO. AVERAGE kinetic energy af ALL of the gas particles depends on the temp. Can not determine the K. E. of each particle based on temperature.
Ideal vs. Ideal vs. RealReal Gases Gases (continued)
Measuring Measuring PressurePressure
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 An Early BarometerBarometer
The normal pressure due to the atmosphere at sea level can support a column of mercury that is 760 mm high.
The Aneroid BarometerThe Aneroid Barometer
The Digital BarometerThe Digital Barometer
Standard Temperature and Standard Temperature and PressurePressure
““STPSTP””
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.
BoyleBoyle’’s Laws Law**
Pressure Volume = Constant (k) P1V1 = P2V2 (T = constant)
Pressure is inversely proportional to volume when temperature is held constant.
A Graph of BoyleA Graph of Boyle’’s s LawLaw
Why Don’t I Get a Constant Value for PV = k?
1. Air is not made
of ideal gases2. Real gases deviate from ideal behavior at high pressure
Jaques Charles (1746-1823Jaques Charles (1746-1823)
French Physicist Conducted the
first scientific balloon flight in 1783
CharlesCharles’’s Laws 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
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.
Gay LussacGay Lussac’’s Laws Law
The pressure and temperature of a gas are directly related, provided that the volume remains constant.
2
2
1
1
T
P
T
P
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
DaltonDalton’’s Law of Partial Pressuress 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.
Standard Molar Standard Molar VolumeVolume
Equal volumes of all gases at the same temperature and pressure contain the same number of molecules.
- Amedeo Avogadro
Standard Molar VolumeStandard Molar Volume
Remember the mole triangle??
Ideal Gas LawIdeal Gas Law
PV = nRT P = pressure in atm
• V = volume in liters T = temperature in Kelvins
n = moles • R = a constant
= 0.0821 L atm/ mol·
Holds closely at P < 1 atm
What is R?
If PV = nRT and
P = atm V = liters n = moles T = Kelvins
R = PV SO R = atm x L
nT mol x K
End of Slide Show