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