Thermodynamics: Calorimetry
How are you feeling? How do you feel about yourself as far as this class goes? How smart/prepared/good at physics do you feel like you are? A) I m in the top third B) I m in the middle third C) I m in the bottom third
From Warmup This section of the reading was a lot easier than the others! Phew! I feel like when I read the assigned sections all of the information just goes in one ear and out the other. I feel like I'm not processing it or fully understanding what is going on in the reading. do you have any tips on what to do to get more out of the reading? Will a study guide/ previous exams be provided before each test? What is temperature? Temperature is a measure of how readily something gives away or absorbs thermal energy. (It is not the energy itself.)
In-class warmup A B A block of material A at 0 C and a block of material B at 100 C are in contact. Initially they have different temperatures. After a while they come to equilibrium. The final temperature is: A) 100 C B) 0 C C) 50 C D)???
Three ideas to focus on today 1. Heat 2. Specific Heat 3. Latent Heat What do all three of these have in common?
Discuss with your neighbor: What is heat? What is internal energy? What is meant by the mechanical equivalent of heat? (and what is a better way of saying that?)
Energy vs. Heat From Warmup: How come saying the "heat" of the sidewalk is incorrect? Isn't the heat that you feel a change in internal energy of the sidewalk, thus it can be accurately described as heat? Internal energy = all the energy of the system associated with its internal components Heat = transfer of internal energy due to temperature differences Analogy Heat : Internal Energy :: Work : Mechanical Energy
Equivalence between mechanical energy and internal energy
Heat Capacity/Specific Heat From Warmup: Heat Capacity the the thermal energy needed to heat a sample by a degree in temperature. Specific Heat is the the Heat Capacity of a one unit mass of a certain subject. So, while Heat Capacity is different between an ice cube and a hockey rink, the Specific Heat is not. Heat capacity is the thermal energy required to raise an object of some masse by 1 degree Celsius, where specific heat is the thermal energy required to raise 1g of the same substance by 1 degree Celsius.
Specific Heat for different substances Using your book, answer the following: You have three objects of equal mass all at the same temperature. One is made of iron, one is made of glass, one is made of ice. If you transfer 123 J of energy to each one, which will have the highest final temperature? A) Iron B) Glass C) Ice If the temperature of each is changed by 23 C, which absorbed the most energy? A) Iron B) Glass C) Ice
Latent Heat What is it? Where does the energy go, if not into changing the temperature? From Warmup: The energy is going towards the phase change, towards breaking bonds...right? Heat is being added at B and D, but the temperature is not increasing because the energy of the heat is being used to change the ice to water and the water to steam. So the energy isn't lost, it is just used to break up the bonds of the molecules in the ice or water to change them to water or steam.
Phase Transitions/Microscopic Descriptions From Warmup: What does state changing look like on a molecular level? I understand that the molecules increase velocity, spread out, and move around more, but why/how does that change the appearance from a liquid to a gas? What is vibration energy and how is it different from kinetic energy? Vibration energy sounds like moving things so it makes me think it would be kinetic energy.
Boiling water at room temperature Demo How does this work?
How does this work? Video
Superheating/Cooling From Warmup: Why does water require some disturbance in order to freeze or vaporize? How is super-cooling and superheating possible? (Video)
Evaporative Cooling Latent heat of a liquid is drawn into the air Perspiration Swamp Cooler A swamp cooler (more formally called an evaporative cooler) is essentially a large box-like frame containing a big fan and walled in by water-wetted pads, usually made of cedar shavings or cellulose. The fan whooshes the hot outside air through the dripping pads (which are continually soaked by a water pump), cooling the air by about 20 ºF as the air evaporates water molecules from the pads. The fan then blows the water-cooled air through the house and out a deliberate vent. How well will this operate on a very humid day?