Thermodynamics – branch of physics concerned with the study of both thermal and mechanical (or dynamical) concepts. Application: Steam Engines in 1800’s Figure from: Figure from: http://fwallpapers.com/view/steam-engine-2 Topics Today: Internal Energy, Heat, and Work
Heat is defined as the transfer of energy across the boundary of a system due to a temperature difference between the system and its surroundings. What are the SI units of heat? Internal energy is all the energy of a system that is associated with its microscopic components—atoms and molecules—when viewed from a reference frame at rest with respect to the center of mass of the system. Internal does not include bulk kinetic energy of the system.
Equivalence between mechanical energy and internal energy Figure adapted from Serway and Jewett, Physics for Scientists and Engineers, 8th ed.
Example: An 80 kg person jumps off a 10 m high dive. How many calories are produced as the water stops the person?
Example: A 70 g piece of aluminum (c = 0.215 cal/g°C) at 100°C is dropped into 100 g of water at 0°C. Find the final temperature.
If equal amounts of heat are transferred into two containers of water and the resultant temperature change of the water in one container is twice that of the water in the other container, what can you say about the quantity of water in the two containers? One container contains four times as much water. One container contains twice as much water. Both containers contain the same amount of water. I need more information before I can say anything.
Two bodies that are not in thermal equilibrium initially are placed in intimate contact. After a while the temperature of the cooler one will rise the same number of Kelvins as the temperature of the hotter one drops. amount of thermal energy contained by both bodies will be equal. specific heats of the bodies will be equal. thermal conductivity of each body will be the same none of the above.
Everyone who has ever walked barefoot on a beach in summer has noticed how fast the sand gets hot in the morning. That’s because the sand has a light color. fairly low specific heat. fairly high specific heat. high thermal conductivity. low latent heat of fusion. none of these.
Example: A 2 kg lead ball (c = 128 J/kg°C) at 30°C is placed on a large piece of ice (Lf = 3.33 x 105 J/kg). How much ice melts?
From the graph below, determine the latent heat of fusion of H20. Figure adapted from Serway and Jewett, Physics for Scientists and Engineers, 8th ed.
An open beaker of pure water is gently boiling at atmospheric pressure An open beaker of pure water is gently boiling at atmospheric pressure. A thermometer held deep in the water will likely read a temperature a little greater than 100C. equal to 100C. equal to 212C. a little less than 100C. none of these.
An open pot of water is boiling on a gas stove when someone raises the flame. The result will be A substantial increase in the temperature of the water. An decrease in the pressure of the water. An increase in the rate of boiling. An appreciable increase in both the rate of boiling and the temperature of the water. None of these.
Five pound of ice in a cooler will keep things cold longer than five pounds of ice water because the ice is colder than the water. the specific heat of ice is greater than the specific heat of water. five pounds of ice has more volume than five pounds of water. the heat capacity of water is less than the heat capacity of ice. none of the above.
When you put water at about 25C into an ice tray and freeze it in the refrigerator, more heat is removed in bringing the water to the freezing point than is removed in the freezing process. more heat is removed in the freezing process than in bringing the water to the freezing point. about equal amounts of heat are removed in brining the water to the freezing point and in freezing the water.
From the graph below, determine the latent heat of vaporization of H20. Figure adapted from Serway and Jewett, Physics for Scientists and Engineers, 8th ed.
Can you boil water over a flame in a paper cup? yes. no. YOU MUST BE NUTS!
Work done by a gas: Work done on a gas: Ask about the negative sign and what this represents.
Example: An ideal gas expands from 2.0 m3 to 3.0 m3 at constant temperature. What is the work done by the gas?
Below are plots of pressure vs Below are plots of pressure vs. temperature for a system that was taken from an initial state, i, to a final state, f, along 3 different paths (i.e. in 3 different ways).
Was positive work done on or by the system?
Which path leads to the most work done on the system?
You are planning a birthday party for your niece and need to make at least 4 gallons of Kool-Aid, which you would like to cool down to 32 oF (0 °C) before the party begins. Unfortunately, your refrigerator is already so full of treats that you know there will be no room for the Kool-Aid. So, with a sudden flash of insight, you decide to start with 4 gallons of the coldest tap water you can get, which you determine is 50 °F (10 °C), and then cool it down with a 1-quart chunk of ice you already have in your freezer. The owner's manual for your refrigerator states that when the freezer setting is on high, the temperature is -20 °C. Will your plan work? You assume that the density of the Kool-Aid is about the same as the density of water. You look in your physics book and find that the density of water is 1.0 g/cm3, the density of ice is 0.9 g/cm3, the heat capacity of water is 4200 J / (kg °C), the heat capacity of ice is 2100 J / (kg °C), the heat of fusion of water is 3.4 x 105 J/kg, and its heat of vaporization is 2.3 x 106 J/kg.