NOTES 24 - Topic 3 - Thermal Physics

1. NOTES 24 - Topic 3 - Thermal Physics ----------------------------------------------------------------------------------- 3.2.3 Phases of Matter; BEC (Bose-Einstein Condensate) - atoms at extremely low temperature (1.00 x 10-9 K); lose individual identities and behave as a single “superatom” with identical motions and movements...the matter counterpart of the laser; predicted in 1925 by Nath Bose and Albert Einstein; produced in 1995 at JILA in Colorado; Solid - definite shape; definite volume; almost incompressible; diffusion is small; comparative density is high; KE of molecules/atoms is vibrational; PE of molecules/atoms is high; Liquid* - indefinite shape; definite volume; slightly compressible; diffusion is slow; comparative density is high, but lower than a solid; KE of molecules/atoms is vibrational, rotational, and some translational; PE of molecules/atoms is higher than solid; spacing between molecules/atoms much greater than in solids; Gas* - indefinite shape; indefinite volume; highly compressible; diffusion is fast; comparative density is low; KE of molecules/ atoms is vibrational, rotational, but mostly translational; PE of molecules/atoms is higher than liquid; spacing between molecules/atoms much greater than in liquid; Plasma* - caused by heating a gas to the point where electrons are stripped from the nuclei; contains only charged particles (nuclei and electrons); most matter in the universe is in the plasma state (ie., stars); [*liquids, gases, and plasmas are also called fluids]

2. 3.2.4 Phase changes in terms of molecular behavior 1. As temperature increases, molecular motion (kinetic energy) increases; 2. As KE increases, the average molecular kinetic/thermal energy becomes comparable to the intermolecular binding energies that hold the molecules/atoms in phase; the occurs up to the “phase-change-temperature” (ie., MP, BP, IP); 3. As more energy is added to the material, the energy is absorbed as internal energy, the intermolecular binding energies are overcome, and molecules/atoms move from their current state/phase to the next state/phase; 4. Thus, a solid changes to a liquid, a liquid to a gas, and a gas to a plasma. Phase Transition by Element http://lectureonline.cl.msu.edu/~mmp/period/phase.htm

3. 3.2.5 Temperature does not change during a phase change When a substance reaches a phase change temperature... 1. it’s temperature stops rising; 2. any additional heat absorbed by the substance increases the internal energy of the molecules; 3. when internal energy is higher than the binding energy holding the molecules in place, the molecules break away from the substance; 4. temperature of the substance remains at its phase change temperature as long as it is in the lower energy phase; 5. heat absorption takes place with no temperature change... the heat is said to be “hidden” or latent.

4. Phase Change Diagram (aka a Heating Curve) for Water Temperature as a Function of Heat Added Notice... 1. “zero-slope” sections where phase change takes place; 2. length of the “zero-slope sections is directly related to the amount (mass) of the material; 3. sections with positive slope are the temperature-change sections. 4. slope of the curve is indirectly related to the specific heat of the material (ie., the steeper the slope, the greater the temperature change, and thus the lower the specific heat of the material). Temperature (K) Heat (J)

6. 3.2.6 Evaporation vs Boiling EVAPORATION - the change of a liquid to a gas at a temperature lower than BP; • Temperature is a measure of the average KE of the molecules of a material; • Some molecules will have high KE and some low KE; • Molecules with high KE near the liquid’s surface may break through the surface tension and become a gas; • Those molecules which break through and become a gas take their high KE with them; • As high KE molecules break through the surface tension and become gas, the average KE of the material decreases and so does the temperature...this is poorly named “evaporative cooling”, and will be called evaporative temperature reduction in this class; • A substance which evaporates rapidly at a particular temperature is said to be volatile; BOILING - the change of a liquid to a gas at its BP; • Energy is added to a liquid and the temperature of the material increases to the BP; • At the BP, KE stops increasing and any added energy is absorbed as PE; • When enough energy has been absorbed, the vibrational motions of the molecules is great enough to break the molecular bonds holding it in the liquid phase; • The molecules escape from the liquid as a gas;

7. 3.2.10ii Thermal Problems: (you may copy and paste the problems into your Notebook; the solutions must be handwritten in your NB; be sure to leave adequate space...some solutions are long!!) 1. During exercise, a person generates 180. Kcal of heat in 30.0 minutes. If the heat is dissipated by the evaporation of sweat (water) from the skin, what minimum mass of water is lost from the body? (hint: assume water is raised to BP and then boiled) Given: Unknown: Equation:

8. 2. One cube of ice is taken from a freezer at -8.50oC and placed in a 0.100 Kg aluminum calorimeter filled with 0.300 Kg of water at room temperature (20.0oC). The final situation is observed to be all water at 17.0oC. Determine the mass of the ice cube. Given: Unknown: Equation:

9. 3. The specific of elemental mercury (a liquid at room temp.) is 138 J Kg-1oK -1. Determine the latent heat of fusion of mercury using the following calorimeter data: 1.00 Kg of solid Hg at its melting point of -39.5oC is placed into a 0.620 Kg aluminum calorimeter with 0.400 Kg of water at 12.80oC. After the Hg as melted, the final temperature of the system is 5.06oC. Given: Unknown: Equation:

10. 4. At a crime scene, a forensic investigator observes that a 8.2 g lead bullet stopped by a wooden door-frame melted upon impact. Assuming the bullet was fired at room temperature (20.oC), what was the minimum muzzle velocity of the bullet as it left the gun? Given: Unknown: Equation: