Chapter 15 Kinetic Theory

REVIEW

STATES OF MATTER•Solid, Liquid & Gas

INTERMOLECULAR FORCES•Account for:

•surface tension•capillary action•Melting/boiling points

Bond Type IMF Strength State of Matter

Ionic Electrostatic forces

Extremely strong b/c attracting opposite

chargesSolids

PolarCovalent

Hydrogen bonding

Strong b/c of large electronegativity

differenceLiquids

Dipole-dipole

Medium b/c of polarity (partial charges)

NonpolarCovalent

LondonDispersion

Forces

Weakest b/c no charges Gases

INTERMOLECULAR FORCES

•Account for:•surface tension•vapor pressure•capillary action•chromatography•Melting/boiling points

KINETIC - MOLECULAR THEORY OF GASES

THE NATURE OF GASES

•The word “Kinetic” means motion•The energy an object has due to its motion is called kinetic energy

•The kinetic theory states that tiny particles in all forms of matter are in constant motion!

3 BASIC RULES OF THE KINETIC THEORY FOR GASES:

1) Gas is made of particles (usually molecules/atoms)

• Small, hard spheres• Insignificant volume• Relatively far apart from

each other• Little/No attraction or

repulsion between particles

3 BASIC RULES OF THE KINETIC THEORY FOR GASES:

2) Particles in a gas move rapidly in constant random motion• Move in straight paths• Change direction only when colliding

with something else• Average speed of O2 in air at 20oC is

an amazing 1660 km/h!

3 BASIC RULES OF THE KINETIC THEORY FOR GASES:

3) Collisions are perfectly elastic• meaning kinetic energy is transferred

without loss from one particle to another• the total kinetic energy remains constant• no energy is lost between particles• bounce off each other without sticking

GAS PRESSURE- defined as the force exerted by a gas per

unit surface area of an object• Due to:

a) force of collisions b) number of collisions

What about when NO particles are present?• Then there cannot be any collisions, and

thus no pressure called a vacuum

GAS PRESSURE

Atmospheric pressure is the amount of force the weight of the atmosphere exerts per square inch• Decreases as you climb a mountain

because the air layer thins out as elevation increases

Barometer is the measuring instrument for atmospheric pressure; dependent upon weather

STANDARD TEMPERATURE AND PRESSURE (STP)

For gases, it’s important to relate measured values to standards:•Standard conditions for gases are a temperature of 0oC and a pressure of 1 atm

KELVIN SCALE

Kelvin is a unit of temperature, like Celsius or Fahrenheit

Zero on the Kelvin Scale is the theoretical temperature at which ALL MATTER STOPS MOVING. This is called Absolute Zero.