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qsNst-6SB0c-096|Those are also called irreversible processes. |
qsNst-6SB0c-097|That is, we never observe the reverse process happening by itself. |
qsNst-6SB0c-098|Now, that doesn't mean we can't make the reverse process happen. |
qsNst-6SB0c-099|You know we could create a system that would have a piston, and push all these gases back to one side, and evacuate this side. |
qsNst-6SB0c-100|But in doing so, we'd have to bring energy in from the surroundings. |
qsNst-6SB0c-104|That is, the systems and surroundings just balance each other out. |
qsNst-6SB0c-105|Or there there's no change in entropy in the system and the surroundings. |
qsNst-6SB0c-106|That would be saying that each side of a chemical reaction is equally likely. |
qsNst-6SB0c-107|That is, there's no entropy penalty for being on one side or the other side. |
qsNst-6SB0c-108|I can be a reactant or I can be a product. |
qsNst-6SB0c-109|Going between the two, there's no entropy change of the universe. |
qsNst-6SB0c-110|So it's equally likely that I'm at either side. |
qsNst-6SB0c-111|That's the definition of equilibrium. |
qsNst-6SB0c-112|If it's equally likely for me to be here or here, no energy penalty, then I'll switch between the two freely. |
qsNst-6SB0c-113|I'll be at equilibrium. |
qsNst-6SB0c-114|Now, entropy decreasing in the universe, those processes are not possible. |
qsNst-6SB0c-115|So now, we have a thermodynamic parameter that will tell us the direction of things. |
qsNst-6SB0c-117|It's entropy that determines the favored direction in the universe. |
wFY9ZvUmM5o-000|So we've learned that light has a particle nature. |
wFY9ZvUmM5o-001|There's a wave property associated with light and electromagnetic radiation, and also a particle nature-- packets of energy being carried along the wave. |
wFY9ZvUmM5o-002|A brilliant experiment that demonstrates that property is the photoelectric effect. |
wFY9ZvUmM5o-003|And here's how it works. |
wFY9ZvUmM5o-004|You take a piece of metal. |
wFY9ZvUmM5o-005|Now metal is an array of metal atoms, and each of those atoms holds on rather loosely to its outer electrons. |
wFY9ZvUmM5o-006|That's why the metal conducts electricity. |
wFY9ZvUmM5o-007|Those electrons are rather free to move about the surface. |
wFY9ZvUmM5o-008|Now, if you shine light on that surface, what happens? |
wFY9ZvUmM5o-012|And even if you make the light very bright, very intense, nothing happens. |
wFY9ZvUmM5o-015|It's as if photons are striking electrons and kicking them off the metal. |
wFY9ZvUmM5o-016|You bring in a more intense green light, and you get more electrons. |
wFY9ZvUmM5o-017|They don't go away faster. |
wFY9ZvUmM5o-018|You just get more electrons with a brighter light, all with the same kinetic energy. |
wFY9ZvUmM5o-020|And again, the same correlation with brightness-- if you make the light brighter, you get more electrons per second released. |
wFY9ZvUmM5o-025|So it doesn't matter if there's more of them. |
wFY9ZvUmM5o-028|More energy still in blue photons ejects electrons with even more kinetic energy. |
wFY9ZvUmM5o-029|So it's as if the photons of light are coming in and jostling electrons. |
wFY9ZvUmM5o-030|I'm holding onto this tennis ball. |
wFY9ZvUmM5o-031|Photons are coming in and jostling them. |
wFY9ZvUmM5o-033|Can I have my tennis ball back? |
wFY9ZvUmM5o-035|Now brightness doesn't matter. |
wFY9ZvUmM5o-036|We said, well, brightness is just more photons per second. |
wFY9ZvUmM5o-037|That's just peh, peh, peh, peh, peh, peh, peh, peh, peh, peh, peh, peh, peh, peh-- but not enough energy-- one photon per electron to eject any single electron. |
wFY9ZvUmM5o-038|But big photons, high energy, blue light, say, comes in and slams that metal and really sends the electron flying. |
wFY9ZvUmM5o-039|[SOUND OF BALL HITTING OBJECTS] CREW: Ow! |
wFY9ZvUmM5o-041|[LAUGHS] Sorry, guys. |
wFY9ZvUmM5o-042|[LAUGHS] High energy is what we have. |
wFY9ZvUmM5o-043|So we can actually plot it. |
wFY9ZvUmM5o-051|So all the excess energy of the photon goes into kinetic energy. |
wFY9ZvUmM5o-052|So you can write the both energies in terms of photons. |
wFY9ZvUmM5o-053|And you can realize there is a minimum photon energy required to eject the electron from the metal. |
wFY9ZvUmM5o-054|If you look at different metals, different metals have different threshold frequencies. |
wFY9ZvUmM5o-055|For instance, you could have a metal that's described by a blue photon is the minimum photon that ejects an electron. |
wFY9ZvUmM5o-058|And it's actually Albert Einstein, a genius, who looked at this problem. |
wFY9ZvUmM5o-060|But increasing the intensity-- very bright light-- didn't do anything. |
wFY9ZvUmM5o-061|And when you could eject electron, increasing the intensity didn't increase the energy of the electrons. |
wFY9ZvUmM5o-062|You just got more electrons coming off with the same energy. |
wFY9ZvUmM5o-063|Well, it takes a genius, often, to look at a very troubling problem and see it in a whole new light. |
wFY9ZvUmM5o-064|And that's what Einstein did. |
wFY9ZvUmM5o-065|He said, well, that looks like the light's behaving like particles. |
wFY9ZvUmM5o-066|It looks like little bits of light are coming in. |
wFY9ZvUmM5o-067|So a bright light is just lots of bits. |
wFY9ZvUmM5o-068|But they all have the same energy. |
wFY9ZvUmM5o-069|So those lots of bits eject lots of electrons, each electron with the same energy. |
wFY9ZvUmM5o-070|So the photoelectric effect and Albert Einstein have helped us understand the particle nature of light. |
_56-KofIBng-000|Let's do a calculation with electromagnetic radiation, the properties of wavelength and frequency. |
_56-KofIBng-001|What frequency and designation of radiation, with wavelength 8.83 picometers, is emitted from Technetium 99 during its nuclear decay? |
_56-KofIBng-002|So, we understand a wavelength, 8.83 picometers. |
_56-KofIBng-003|We can change that into a frequency knowing that the waves travel at the speed of light, c. |
_56-KofIBng-010|So very, very, very high frequency. |
_56-KofIBng-011|Very short wavelength, as we'd expect. |
_56-KofIBng-012|What region of the electromagnetic spectrum does that correspond to? |
_56-KofIBng-014|So we have gamma waves emitted from technetium 99 during its nuclear decay. |
j7ROvrT6W1M-000|The polymerization of ethylene to polyethylene is taking individual monomers of ethylene and making a polymer. |
j7ROvrT6W1M-001|Polymer means many elements. |
j7ROvrT6W1M-002|That term poly means many. |
j7ROvrT6W1M-015|So that's a wash, equal energy for breaking and making. |
j7ROvrT6W1M-016|So if I break, let's say, just three carbon-carbon double bonds, how many single bonds do have to make to hook the chain together? |
j7ROvrT6W1M-018|You're breaking N carbon-carbon double bonds and making 2 N, twice as many carbon-carbon single bonds. |
j7ROvrT6W1M-019|So let's see how that energy balance works. |
j7ROvrT6W1M-022|I get back 700. |
j7ROvrT6W1M-024|The difference between those is a net release of energy. |
1lHCPo6GH3I-000|Let's look at forming some molecular orbitals from atomic orbitals. |
1lHCPo6GH3I-004|Negative signs and positive signs in the wave function gives zero somewhere in the middle. |
1lHCPo6GH3I-005|So that mathematical combination will give me a node right between the two atoms. |
1lHCPo6GH3I-006|That's not very good for bonding, that will be high energy. |
1lHCPo6GH3I-009|So the highest energy will be the most nodes, the node right between the nuclei. |
mKzVNK6FeKQ-000|Let's look at a common process-- a gas expanding adiabatically-- quickly-- against a constant pressure. |
mKzVNK6FeKQ-001|If the gas expands adiabatically against constant pressure, what happens to the temperature of the gas? |
mKzVNK6FeKQ-007|We're talking about the adiabatic expansion of an ideal gas against a constant pressure. |
mKzVNK6FeKQ-008|And this system is like discharging an aerosol can. |
mKzVNK6FeKQ-009|The gas expands out the nozzle of the can and pushes back the atmosphere. |
mKzVNK6FeKQ-013|The system does work, uses its internal energy. |
mKzVNK6FeKQ-014|If I use my internal energy, my internal energy goes down. |
mKzVNK6FeKQ-015|If I'm a gas, a drop in internal energy always is accompanied by a drop in the temperature. |
mKzVNK6FeKQ-016|So here, the temperature decreases. |
mKzVNK6FeKQ-017|And you can try this at home. |
mKzVNK6FeKQ-018|Discharge an aerosol can and feel the top of the can. |
mKzVNK6FeKQ-019|It will be colder. |
qhg-pZ-f-PM-000|Biology and chemistry are intimately related, because we understand biology now in terms of the molecules of biology. |
qhg-pZ-f-PM-001|And molecules are, of course, the purview of chemistry. |
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