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August 6, 2013
Published by Bryan at August 6, 2013
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When I start into heat capacity I contrast the temperature of a substance with the feeling of hot and cold. A thermometer will tell you the temperature of a substance, but that does not tell you how much heat is present. If you touch something, you can tell if it is hotter or colder than your hand, but what about two substances at the same temperature?
Suppose outside it is -10 C (14 F) and there you find a piece of steel and a piece of Styrofoam. Which is colder? If you touch the steel it feels colder than the Styrofoam, but they are both at the same temperature. If you placed the steel on the Styrofoam, no heat will flow between them (Third Law of thermodynamics). Since your hand is much hotter than the objects, heat must flow from your hand into them.
July 25, 2013
Published by Bryan at July 25, 2013
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One question I pose every year to my physical chemistry class of life science students in the first lecture is “Where is chemical energy stored?” Almost all of them say in chemical bonds. Ask how the energy is released, and they say “When bonds are broken.”
Wrong!
December 19, 2011
httpvh://youtu.be/wFe2zu2116I After rolling 2, 3, 4, 10 and Avogadro’s dice, as seen in the entries below, it becomes clear that the most random states (most number of ways of rolling a number) always dominate while those with fewer arrangements occur less frequently: 1 Entropy: Randomness by rolling two dice 2 […]
December 12, 2011
With Avogadro's number of dice, you can roll them as much as you want, and the chance that there is an outcome other than the one that corresponds to the position of the spike is so unlikely you can safely ignore them.
December 5, 2011
For 10 dice there are over 60 million arrangements and Figure 1 shows the outcomes for 30,000 rolls.
November 21, 2011
The basic idea is that a physical system has many different arrangements (states) of particles which are consistent with some macroscopic quantity, like the temperature. Boltzmann found that out of all possible ways those particles can be arranged, only those that are consistent with the actual temperature need be considered. The chance of any other arrangements is negligible in comparison. Rolling dice illustrates this nicely.
November 8, 2011
To understand entropy, I roll dice. I start with two, then move to three, four, ten and then Avogadro’s constant of dice, and roll them randomly.
July 15, 2011
Published by Bryan at July 15, 2011
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The more heat that is converted into work, the more efficient the process. The heat lost to the cold reservoir cannot be recovered. Efficiency is therefore define as the ratio of work out to heat in,...
July 13, 2011
Published by Bryan at July 13, 2011
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The Third Law of Thermodynamics says: if two separated systems are in thermal contact with a third, then at equilibrium they all have the same temperature.
Clearly when we bring two blocks together, heat will flow between them. This is an example of coupling systems A to B and to C so eventually the three will be in equilibrium. This coupling only allows heat to flow through direct contact.
July 11, 2011
Published by Bryan at July 11, 2011
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Suppose we have a system which is a drink in a glass. Certainly heat flows in and warms the cold drink, and mass changes when we add to the glass or drink the contents. The system is open.
June 30, 2011
Published by Bryan at June 30, 2011
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First it is never possible to obtain a true reversible path. It is an idealized case in which at every step along the way the system (the ball) is in equilibrium with its surroundings. Clearly if something is at equilibrium there is no noticeable change. Hence one says that a reversible process happens so slowly that equilibrium is always maintained.
June 2, 2011
Published by Bryan at June 2, 2011
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Another way to ask the same question: suppose you have eaten all the food you need to keep your metabolism and daily activity going, but then you have one cookie too many. How much fat will that put on you?