After our Ideal Gas quiz, we accounted for the fact that temperature of ice does not change as energy is added to it while it melts to liquid water at 0˚C. We know that the energy added results in separation of water molecules from each other to some extent. The question remains, though, Where is this energy once the water is melted and at 0˚C? You should know the answer to that question by now.
After today you should also know why it takes so much more energy to vaporize 1 kg of water than to melt one 1 kg of water. And even at 100˚C, 1 kg of water vapor has much, much more energy stored in it than 1 kg of liquid water at 100˚C. The big goal for today was to see how attractive particles become bound to each other. This is required for gases to become liquids, for example.
Among other things we want to give a reason for the existence of heats of fusion and heats of vaporization. We can think of condensed matter (solids and liquids) as having a thermal energy system and a "phase energy" system. The thermal energy system is made up of all the jiggling particles and contributes to temperature. Through collisions with its particles, the thermal system can gain energy from or lose energy to its environment. The so-called "phase system" consists of the electric fields enhanced during melting and vaporizong, a process simulated today with our computer simulations. As noted today, these fields take energy to create, and they in fact store this energy. This latent energy is not sensible; it is stored in electric fields, not jiggling particles. When condensing and freezing, particles once again bond, shedding energy to the environment, energy that comes from the now-diminshed elecric fields. The lost latent energy (aka "phase energy" or "field energy") doesn't contribute to temperature, and so there is no change in temperature during a change of phase. The jiggling is just as effective before and after the phase change, which is just another way of saying the temperature doesn't change during the phase change. We confronted a real phenomenon, namely condensation, that cannot be accounted for by the Ideal Gas Model. What to do? Well, water molecules must attract each other in order to stick together. That is NOT a property of the ideal gas model, the particles of which interact only by colliding elastically, not by attracting each other.
Assignment: Today we presented, by random selection of members of our studio audience, our responses to Ideal Gas Model Factors.
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Physics II
Mr. Swackhamer Scottsdale Preparatory Academy Archives
March 2020
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