13-11Kinetic Theory and the Molecular Interpretation of Temperature

•Kinetic Theory…1. There are a large number of molecules, N, of mass m that are tiny,

hard spheres which have constant, straight-line, random motion.2. The molecules are, on average much greater than their diameter

away from each other.3. The molecules interact with each other only when they collide, and

the kinetic force of collisions is much greater than the weak attractive forces.

4. Collisions are perfectly elastic.KE= ½ mv2 = 3/2 KT …KE is directly proportional to Kelvin Temperature.P= (1/3) Nmv2 /V

13-11 cont’d

• See Examples 13-16 and 13-17• Root-mean-square velocities…• Vrms =(v2 )1/2 =(3kT/m)1/2

13-12 Distribution of Molecular Speeds

• Maxwell’s distribution of molecular speeds is basically a bell-curve. See pg. 402.

13-13 Real Gases and Changes of Phases

• Critical temperature is the temperature below which a gas will turn into a liquid if the pressure is right…above that temperature, no pressure can cause the change to occur to liquid.

• Critical point is the one point where a PV diagram has a horizontal line. (see p 404)

• See the triple point diagram p 404• Sublimation refers to the conversion of solid

to gas.

13-14 Vapor Pressure and Humidity

• Evaporation can be explained by kinetic theory.

• Condensation is the reverse process.• Vapor pressure is the pressure above a liquid

in a sealed container.• Partial pressure is the pressure by one gas.• Relative humidity= pp [H2O/ (saturated vp H2O)] x 100%• See Example 13-18

Homework

• P414 47-51, 57-59, 60-63 due Tues BOP