4.b Kinetic Molecular Theory

Kinetic Molecular Theory (KMT) based on the idea that particles are constantly moving can be applied to solid, liquid, or gas Based on energy of particles and forces that act between them

KMT (cont’d) KMT of gases is a model of an ideal gas Hypothetical gas that perfectly fits all the assumptions of the KMT 5 basic assumptions….

#1Gases consist of tiny particles that are very far apart most volume is empty space-low density allows gases to be easily compressed

# 2 All collisions between particles and container walls are elastic there is no net loss of energy when particles collide total KE stays constant  can be transferred between particles

# 3 Particles are in continuous, rapid, random motion since they are moving, they have KE KE overcomes their attractive forces

#4 No forces of attraction or repulsion like billiard balls bounce apart immediately

#5 Average KE depends on Temp KE = ½mv2 where m = mass of particle where v = velocity of particle V, T, & KE are directly proportional So…. KE ↑’s as T↑’s & V↑’s at the same T, lighter particles have higher speeds than heavier ones

KMT and Nature of Gases Accounts for Physical Properties of gases…. Expansion – gases do not have a definite shape or definite volume Assumption # 3 & 5 Fluidity – gas particles slide easily past one another Both gases & liquids are knows as fluids Assump #4

Physical Properties cont’d Low Density – density of gas is typically 1/1000 the density of the same substance in the liquid of solid state Compressibility – gas particles may be crowded close together since they are initially so far apart

Physical Properties cont’d Gases spread out and mix with one another even without being stirred Diffusion – spontaneous mixing of particles of 2 substances caused by random motion Why smells spread out