Thermal physics Temperature scales Celsius (Centigrade) Kelvin Fahrenheit Warmest and coldest places in universe? Demo: flaming jar

Thermometers Expansion Thermocouples Resistors Semiconductor devices Infrared thermometers

Ideal gases Molecules collide like billiard balls due to repulsive forces No attractive forces Never condense into liquids or solids, at any T or P Don’t exist Essentially ideal gases:

Essentially ideal gases

Thermodynamics Describe behavior of huge numbers of particles in terms of macroscopic variables like P, T, V, N Experiments on ideal gasses, varying T, P, N

Ideal gas law k­ B = x J/ºK Boltzmann’s constant N is number of molecules n is number of moles of molecules 1 mole =6.02x10 23 Avagadro’s number (N A ) = J/moleºK = liter-atm/moleºK

In an engine piston, with air at 1 atm, the volume is decreased from 200 cm 3 to 40 cm 3, while the temperature increases from 300 K to 600 K. Find the final pressure.

Use “absolute” T and P! …whenever T or P are multiplied or divided. Absolute T is simply the Kelvin scale. Absolute P vs gauge P:

A spray can is “empty” (gauge pressure is 0), at 20 C, room temperature. You throw it into the fire at 600 C. P1. Knowing that N and V are constant, what is the final absolute P in the can (if it doesn’t burst)? _____ atm A: 0 B: 0.73 C: 2.98 D. 15.3E: 30 What is the final gauge pressure?

Liquid to gas A spray can is has a few grams of liquid, at 20 C, room temperature. You throw it into the fire at 600 C. Does the liquid matter?

Where pressure comes from

Molecular view Average kinetic energy Average thermal velocity Pressure and velocity: Then P total is proportional to: (ideal gas law)

You have a mixture of equal numbers of heavy and light molecules in an ideal gas. P2. The molecules that move the fastest are: A.heavy B.light C.same P3. The ones that exert the most pressure are: (check ideal gas law) A.heavy B.light C.same P4. One molecule has molecular weight of 10.0 g/mol. Another has a weight of 40.0 g/mol. If they are mixed, the ratio of average speeds ( v fast /v slow ) is A. 1.0 B. C. 2 D. 4 E. 8