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Honors Chemistry

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: All matter is composed of small particles

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Honors Chemistry

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  1. Honors Chemistry Chapter 15 Kinetic Theory

  2. 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: • All matter is composed of small particles • The particles are in constant motion • All collisions are perfectly elastic • There is no change in total kinetic energy of the 2 particles before & after their collision

  3. 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

  4. 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

  5. 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

  6. 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 betwatomos & contained gas • If density of liquid is known, press diff can be calculated

  7. 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

  8. 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

  9. 15.3 Measuring Pressure • Types of manometers:

  10. 15.3 Measuring Pressure • Mercury Barometer:

  11. 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 • avgK.E. of particles in a gas is same for all particles @ a certaintemp • 2 gases @ same temp., particles have = K.E.

  12. 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

  13. 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

  14. 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. 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

  16. 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

  17. 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

  18. 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 • Molecsubsts – held together by van der Waals forces • Weaker than ionic bonds

  19. 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

  20. 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

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