Collisions of Gas Particles Collisions of Gas Particles

Collisions of Gas Particles

Collisions of Gas Particles

Kinetic Theory

Kinetic Molecular Theory Postulates of the Kinetic Molecular Theory of Gases 1. Gases consist of tiny particles (atoms or molecules) 2. These particles are so small, compared with the distances between them, that the volume (size) of the individual particles can be assumed to be negligible (zero). 3. The particles are in constant random motion, colliding with the walls of the container. These collisions with the walls cause the pressure exerted by the gas. 4. The particles are assumed not to attract or to repel each other. 5. The average kinetic energy of the gas particles is directly proportional to the Kelvin temperature of the gas

Kinetic Molecular Theory (KMT) Ø explains why gases behave as they do Ø deals w/“ideal” gas particles… 1. …are so small that they are assumed to have zero volume 2. …are in constant, straight-line motion 3. …experience elastic collisions in which no energy is lost 4. …have no attractive or repulsive forces toward each other 5. …have an average kinetic energy (KE) that is proportional to the absolute temp. of gas (i. e. , Kelvin temp. ) AS TEMP. , KE

Elastic vs. Inelastic Collisions 8 3

Elastic vs. Inelastic Collisions v 1 POW v 2 8 elastic collision v 3 v 4 8 inelastic collision

Elastic Collision v 1 8 before 8 after v 2

Model Gas Behavior • All collisions must be elastic • Take one step per beat of the metronome • Container – Class stands outside tape box • Higher temperature – Faster beats of metronome • Decreased volume – Divide box in half • More Moles – More students are inside box q q q q Mark area of container with tape on ground. Add only a few molecules of inert gas Increase temperature Decrease volume Add more gas Effect of diffusion Effect of effusion (opening size)

Kinetic Molecular Theory • Particles in an ideal gas… – – – have no volume. have elastic collisions. are in constant, random, straight-line motion. don’t attract or repel each other. have an avg. KE directly related to Kelvin temperature. Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

Molecular Velocities Fractions of particles molecules sorted by speed many different molecular speeds the Maxwell speed distribution speed http: //antoine. frostburg. edu/chem/senese/101/gases/slides/sld 016. htm

Real Gases • Particles in a REAL gas… – have their own volume – attract each other • Gas behavior is most ideal… – at low pressures – at high temperatures – in nonpolar atoms/molecules Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

Characteristics of Gases expand to fill any container. – random motion, no attraction Gases are fluids (like liquids). – no attraction Gases have very low densities. – no volume = lots of empty space Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

Characteristics of Gases • Gases can be compressed. – no volume = lots of empty space • Gases undergo diffusion & effusion. – random motion Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

Properties of Gases Gas properties can be modeled using math. Model depends on: V T P n = = volume of the gas (liters, L) temperature (Kelvin, K) pressure (atmospheres, atm) amount (moles, mol)

Pressure - Temperature - Volume Relationship P V P TT V V P Charles 1 Pa V Va. T Gay-Lussac’s Pa. T Boyle’s ___

Pressure - Temperature - Volume Relationship P n T V Boyle’s 1 Pa V Charles Va. T Gay-Lussac’s Pa. T ___

Pressure and Balloons B When balloon is being filled: PA > P B A When balloon is filled and tied: PA = P B When balloon deflates: PA < P B A = pressure exerted BY balloon B = pressure exerted ON balloon

Balloon Riddle When the balloons are untied, will the large balloon (A) inflate the small balloon (B); will they end up the same size or will the small balloon inflate the large balloon? A B Why? C

Kinetic Theory and the Gas Laws 10 10 (a) (b) (c) original temperature original pressure original volume increased temperature increased pressure original volume increased temperature original pressure increased volume Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3 rd Edition, 1990, page 323 (newer book)