I. Physical PropertiesI. Physical Properties

12.1- Gases12.1- Gases

A. Kinetic Molecular A. Kinetic Molecular TheoryTheoryA. Kinetic Molecular A. Kinetic Molecular TheoryTheory

kinetic-molecular theory: (def) theory of the energy of particles and the forces that act between them; based on idea that particles of matter are always in motion

Kinetic molecular theory describes the motion of an ideal gas

A. Kinetic Molecular A. Kinetic Molecular TheoryTheoryA. Kinetic Molecular A. Kinetic Molecular TheoryTheory

ideal gas: (def) imaginary gas that perfectly fits the assumptions of the kinetic-molecular theory

A. Kinetic Molecular A. Kinetic Molecular TheoryTheoryA. Kinetic Molecular A. Kinetic Molecular TheoryTheory

Particles in an ideal gas…• have no volume.• have elastic collisions. • are in constant, random, straight-

line motion.• don’t attract or repel each other.• have an avg. KE directly related to

Kelvin temperature.

B. Real GasesB. Real GasesB. Real GasesB. Real Gases

Particles in a REAL gas…• have their own volume• attract each other• proposed by van der Waals

Gas behavior is most ideal…• at low pressures• at high temperatures• in nonpolar atoms/molecules

C. Characteristics of C. Characteristics of GasesGasesC. Characteristics of C. Characteristics of GasesGasesGases expand to fill any container.

• random motion, no attraction

Gases are fluids (like liquids).• no attraction

Gases have very low densities.• no volume = lots of empty space

C. Characteristics of C. Characteristics of GasesGasesC. Characteristics of C. Characteristics of GasesGasesGases can be compressed.

• no volume = lots of empty space

Gases undergo diffusion & effusion.• random motion

C. Characteristics of C. Characteristics of GasesGasesC. Characteristics of C. Characteristics of GasesGasesDiffusion: (def) process by which gases spontaneously spread out and mix with

other gases; lighter gases diffuse more quickly

Effusion: (def) process by which gases particles under pressure pass through a tiny opening; lighter gases effuse faster

A. TemperatureA. TemperatureA. TemperatureA. Temperature

ºF

ºC

K

-459 32 212

-273 0 100

0 273 373

32FC 95 K = ºC + 273.15

Always use absolute temperature (Kelvin) when working with gases.

B. PressureB. PressureB. PressureB. Pressure

area

forcepressure

Which shoes create the most pressure?

SI unit of force is the Newton

. Pressure. Pressure. Pressure. Pressure Barometer

• measures atmospheric pressure - at sea level,

height of column is

760 mm

- P of Hg is equal to the P of the atmosphere

Mercury Barometer

E. PressureE. PressureE. PressureE. Pressure

Manometer• measures contained gas pressure

- difference in height of tubes indicates the

gas pressure

U-tube Manometer

E. PressureE. PressureE. PressureE. Pressure

2m

NkPa

KEY UNITS AT SEA LEVEL

101.325 kPa (kilopascal)

1 atm

760 mm Hg

760 torr

14.7 psi

Pressure Pressure Pressure Pressure Unit Symbol Definitions

Pascal Pa SI Pressure Unit;

1 Pa = 1 N/m2

Millimeter of

Mercury

mm Hg P that supports a 1 mm mercury column in a barometer

Atmo-sphere

atm 1 atm = 760 mm Hg

= 101.325 kPa

Torr torr 1 torr = 1 mm Hg

C. STPC. STPC. STPC. STP

Standard Temperature & PressureStandard Temperature & Pressure

0°C 273.15 K

1 atm 101.325 kPa-OR-

STP

D. Dalton’s lawD. Dalton’s lawD. Dalton’s lawD. Dalton’s law

Dalton’s law of partial pressure:

• Ptotal = P1 + P2 + P3…+Pn

(n = number of gases in mixture)

**Total P exerted by collection gases is sum of pressure exerted by each gas