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