1. Thermal Properties of Matter

2. I.Temperature, Heat, Internal Energy and the 0 th Law of Thermodynamics A.Temperature -measure of hot and cold -T is directly related to the average KE of the particles - T ̴̴ KE avg What is kinetic energy KE? - KE = ½ mv 2 = p 2 /2m - higher KE --> faster particles --> higher T - lower KE --> slower particles --> lower T  Absolute temperature scale: Kelvin scale, K What does absolute mean? At absolute zero, 0 K, the particles reach minimum speed If the Kelvin temp doubles, the Ke avg doubles. If the Kelvin temp triples, the Ke avg triples. (atoms and molecules)

4. It just sounds so sad!

5. The Celsius temperature scale, C, has the same size degrees as the Kelvin scale, but it is not “absolute.” 0 0 C = water freezes/melts 100 0 C = water boils/condenses T (K) = T ( 0 C) + 273 Ex. At what Kelvin temps does water melt and condense? Ex. What is 0 K in Celsius degrees?

6. 300 K 400 K Place in contact. In which direction does thermal energy (heat) flow? What 1 factor determines the direction of energy flow? Ex. Suppose you have two objects at different temps. The Second Law of Thermodynamics (Study of Heat): Heat flows spontaneously (naturally) from hotter to colder, and not the other way around. T 300 K 400 K

7. B.What is Heat? definition: Heat is energy that is transferred from one body to another because of a ΔT Ex. Name 3 basic ways that energy can be transferred: conduction, convection, radiation Which way …. …can transfer energy in a vacuum? …must involve direct contact between two bodies? …relies on density differences? Can heat be transferred by all three of these ways? radiation conduction convection

10. So heat is the transfer of energy. Question: What kind of energy? C. Answer: Internal energy = the sum total of all the energy of all the molecules in an object. The internal KE of molecules occurs b/c they can randomly -translate (move in 1 direction) -rotate (spin) -vibrate The internal PE of molecules is there b/c they exert electrical forces on other molecules --> bonding Internal energy = total PE of bonds + random KE of the molecules random KE and PE gravitational PE external KE of molecules X X X For any object:

11. Ex. Which body has molecules with a higher avg KE? 300 K 310 K 300 K Ex. Which body has more internal energy? 310 K

12. Ex. The mechanical equivalent of heat. 4.184 J of mechanical (motional) work done by the falling weight was transferred to the internal KE energy of water, raising the temperature of 1 gram of it by 1 0 C. 4.184 J = 1 calorie Experiment carried out by the English brewer: James Prescott Joule

13. Ex. Is it correct to say the “heat in a body?” No. Heat refers to the transfer of energy, or the amount of energy that is transferred between…. 1. two bodies, or between 2. a body (or “system” of bodies) and its environment. due to a ΔT. This type of energy transfer is called non-mechanical, because the bodies themselves are not exerting forces on each other. In IB, heat is called thermal energy. This means that, in IB, it is also very naughty to use the words, “thermal energy in a body.” Trick IB question: Who has more thermal energy in her, a mommy polar bear at 20 0 C or her cub at 22 0 C? Answer: The mom may have more internal energy, but thermal energy is heat, which is really the transfer of energy

14. And what color is their skin?

15. D. Thermal Equilibrium 300 K 400 K Two objects are said to be in thermal equilibrium if, when placed in contact with each other, 1/ no energy flows from one to the other, and 2/ their temperatures do not change. Place in contact. Wait. What happens eventually? Suppose you start out with two bodies at different temps --> They will reach the same temperature!

16. AC Ex. Suppose C and A are two objects in equilibrium: B C Then you bring C over to B, and they just happen to be in equilibrium, too. What does this tell you about A and B? The 0 th (yes, the zeroth!) Law of Thermodynamics: If two systems (like A and B above) are in thermal equilibrium with a third system (like C above), then they are in equilibrium with each other.  This allows the concept of temperature to be useful, because C could be used like a thermometer.