Honors Chemistry Chapter 15 Kinetic Theory
15.1 Molecules in Motion
� Robt Hooke – explanation of gas behavior ◦ Kinetic Theory – explains the effects of temp
& press on matter
� 3 Basic Assumptions of Kinetic Theory: 1. All matter is composed of small particles 2. The particles are in constant motion 3. All collisions are perfectly elastic � There is no change in total kinetic energy of the
2 particles before & after their collision
15.1 Molecules in Motion
� Many properties of matter are the result of the motion of the particles
� Mean Free Path – the avg distance a molec travels before it collides w/ another molec
� Speed, distance of travel, & # of collisions in a gas vary w/ temp. & mass of the gas particles
15.2 Pressure
� Gas molecs collide w/ the walls of their container as well as other molecs ◦ Exert a force on the container
� Pressure – caused by force & # of collisions w/ the walls of the container ◦ Meas in terms of force per unit area
15.2 Pressure
� Everything is subject to a certain press from molecs of gas in the air ◦ Air press varies from place to place and from
time to time in a particular place
� Standard atmospheric press – avg air press @ sea level ◦ 101.325 kPa (kilopascals) � 1 Pa (pascal) = press of 1 Newton / m2
� Very small press – usually use kPa
15.3 Measuring Pressure
� Manometer – instrument used in measuring gas press ◦ 2 types of manometers: � Open Type – atmos exerts pressure on the column
of liquid in open arm � Studied gas exerts press in other arm � Difference I liquid level betw the 2 arms is a meas of diff in
press betw atomos & contained gas � If density of liquid is known, press diff can be calculated
15.3 Measuring Pressure
� Closed type manometer has a vacuum above liquid in one arm ◦ No press from atmos acting on liquid � Independent of atmos press
� Barometer – closed manometer used to measure atmos press ◦ Most have a scale to read height of Hg in mm
15.3 Measuring Pressure � Standard atmos press – 101.325 kPa will
support a column of Hg 760mm high ◦ ∴101.325 kPa = 760 mm Hg or ◦ 1kPa = 7.5 mmHg � We will use 101.3 for std press
� Closed manometer can meas actual or absolute press ◦ Can calc absolute press w/ open manometer
if atmos press is know ◦ Leave room for examples
15.3 Measuring Pressure
� Types of manometers:
15.3 Measuring Pressure
� Mercury Barometer:
15.4 KINETIC ENERGY AND TEMPERATURE � Avg. speed of particles depends on: ◦ 1. Temp. ◦ 2. mass of particles
� KINETIC ENERGY - energy possess by an obj. bec. of its motion ◦ K.E. = 1/2 m v2 ◦ avg K.E. of particles in a gas is same for all
particles @ a certain temp � 2 gases @ same temp., particles have = K.E.
15.4 KINETIC ENERGY AND TEMPERATURE � @ given temp. particle w/ small mass will
mover faster than particle w/ large mass � Decr. in temp. of subst. means particles
move slower ◦ incr. in temp. - particles move faster
15.4 KINETIC ENERGY AND TEMPERATURE � ABSOLUTE ZERO - temp. @ which all
molec. motion ceases ◦ -273.15 oC (rounded to -273oC)
� KELVIN SCALE - (absolute scale) - zero pt. is absolute zero ◦ K = oC + 273
15.4 KINETIC ENERGY AND TEMPERATURE � Temp. can be used to determine direction
of flow of energy. ◦ flows from high temp. to low temp � explained by kinetic theory
� HEAT - amt. of energy transferred bec. of difference in temp. ◦ meas. in joules
15.5 STATES OF MATTER
� 4 states of matter ◦ kinetic theory used to explain behavior of all
� 1. Gas - particles are independent of ea. other ◦ move in straight lines until collision, then
change direction ◦ travel in randon manner ◦ assume shape & vol. of container
15.5 STATES OF MATTER
� 2. Liquid - particles appear to vibrate around moving point ◦ actually move in straight line betw. near
neighbors ◦ particles can pass over one another ◦ have definite vol. & assume shape of their
container
15.5 STATES OF MATTER
� 3. Solid - particles appear to vibrate around fixed point ◦ actually move in straight line betw. very near
neighbors ◦ particles arranged in definite patterns ◦ have definite vol. & def. shape
15.5 STATES OF MATTER
� Physical state of substs @ room temp & std press depend on the bonding in the substs ◦ Ionic substs – very strong bonds – solids ◦ Molec substs – held together by van der
Waals forces � Weaker than ionic bonds
15.5 STATES OF MATTER
� Polar molec w/ high molec mass tend to be solids
� Nonpolar molecs w/ low melec mass tend to be gases
� The greater the molec mass & greater polarity tend to make substs form condensed states ◦ Solids or liquids
15.6 Plasma
� 4th state of matter ◦ State of matter composed of e-’s & + ions ◦ Most of the universe is made of plasma � Stars
◦ Nuclear rxns (fusion) occur only in plasmas ◦ Since it’s made up of charged particles, it is
affected by electric & magnetic fields ◦ Magnetohydrodynamics – (MDH) – the study
of plasma