GasesCh. 6

Chemistry II

Milbank High School

Kinetic Molecular Theory

All matter is composed of tiny, discrete particles called molecules

They are in rapid, constant motion Move in straight lines

Molecules are small compared to the spaces between them

Little attraction between molecules Molecules collide with one another, and energy is

conserved Temperature is the measure of the average kinetic

energy of gas molecules

Kinetic Molecular Theory Con’t Little attraction between molecules Molecules collide with one another, and

energy is conserved Temperature is the measure of the average

kinetic energy of gas molecules

Properties of Gases

Compressible Low density Don’t settle due to gravity (other than the

density of air) Hot particles move faster

Atmospheric Pressure

Pressure is force per unit area

P = F/A

SI unit for pressure is the pascal (Pa

1 Pa = 1 N / m2

Barometer: used to measure pressure

Pressure Units

1 atm = 760 mmHg = 760 torr = 101.3 kPa = 29.921 in.Hg = 14.696 lb/in2

GAS LAWS

Boyle’s Law

Volume of a gas varies inversely with pressure

PV = PV

Reason gases can be stored in a small volume (high pressure)

Boyle’s Law and Breathing

Inspiration (breathing in)—diaphragm lowered and chest is expanded, increasing the volume of the chest cavity Increased volume = decreased pressure so air

enters from a high pressure area (outside air) to low pressure (lungs)

Charles’s Law

Volume is directly proportional to Kelvin temperature

V/T = V/T

Avogadro’s Law

The volume of a gas is directly proportional to the number of gas molecules present

STP (273 K and 1 atm)

1 mol of gas = 22.4 L

Combined Gas Law

PV/T = PV/T

Just make sure units are the same

Ideal Gas Law

Takes into account different amounts of gases

PV = nRT

n is # of mol R = . 0821 L·atm/mol·K (universal gas

constant)

Henry’s Law

The solubility of a gas in a liquid at a given temp is directly proportional to the pressure of the gas at the surface of the liquid

Pop bottle: bottle is under pressure, when opened the pressure is reduced thus the solubility is reduced (bubbles of CO2 escape)

Henry’s Law and Deep Sea Diving Divers need compressed air Compressed air is much more soluble in blood N2 acts as a narcotic at depths below 30m because

of the increased pressure (Nitrogen narcosis) Decompression sickness (the “bends”)

Bubbles of nitrogen gas in blood and other tissues Occurs when there is a sudden drop in atmospheric

pressure Diver, miners, passengers in airplane

Dalton’s Law of Partial Pressures Total pressure of the gases in a mixture is

equal to the sum of the partial pressures of the separate gases

Ptotal = P1 + P2 +P3 + …..

Gases collected over water Thus contain water vapor Vapor pressure: partial pressure exerted by its

molecules in the gas phase above the liquid phase

Dalton’s Law of Partial Pressures Con’t Humidity: measure of water vapor in air Relative humidity: actual amount of water

vapor compared to amount the air could hold at the temperature

Cool air holds less, thus as temp falls at night, water condenses from the air to form dew

Daltons’ Law of Partial Pressures Con’t Respiration Inspired air: high in O2, low in CO2

Cellular fluid: low in O2, high in CO2

Gases transferred through diffusion Gases flow from an area of high

concentration to an area of low concentration