Chapter 10Chapter 10Physical Characteristics Physical Characteristics

of Gasesof Gases

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

EffusionEffusionEffusion: describes the passage of gas into an evacuated chamber.

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.

The Aneroid BarometerThe Aneroid Barometer

The Digital BarometerThe Digital Barometer

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.

A Graph of Boyle’s A Graph of Boyle’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 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

Relationship of Temperature and Relationship of Temperature and PressurePressure

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

Dalton’s Law of Partial Dalton’s Law of Partial PressuresPressures

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.