Chapter6LEcture

Chapter6LEcture - Chapter 6: Energies in Reactions...

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6 Copyright: 2010 Prof. Magde Chapter 6: Energies in Reactions Thermodynamics This is the study of processes involving heat. Or should I say heating and cooling. Heat is not a thing. It would be best never to use the word as a noun. That was an error 300 years ago with the caloric theory that was very difficult to get past. Try to say heating or cooling Those verbs refer to the transfer of energy in a process that leads to random motion, not organized motion. Random molecular motion. Any transfer of energy that does not lead to random motion is called work. Since chemists deal with molecules more than physicists do, chemists have more need for thermodynamics than many physicists do. Chemical engineers and biologists have even more need.
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6 Copyright: 2010 Prof. Magde Chapter 6: Energies in Reactions • First Law: Energy is conserved. It can be transferred from one place to another, but never created or destroyed. (The full story says that energy can be converted to mass and mass to energy, but that is not important in chemistry.) • We distinguish: SYSTEM , which we are interested in, from SURROUNDINGS , which are everything else. For chemists, the SYSTEM is always molecules or atoms or ions. The SURROUNDINGS include the beaker or flask as well as the room, its air, your hands, and all the rest of the universe. SYSTEM plus SURROUNDINGS = UNIVERSE
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6 Copyright: 2010 Prof. Magde Chapter 6: Energies in Reactions • SYSTEMS have intensive and extensive properties: Extensive properties depend on how big the system is, like mass, volume, moles. Also energy and a bunch of things that have units of energy and are modified energies. Intensive properties apply to each part without having to know about the overall size, like temperature, pressure, color, density, concentration of any molecules or ions. Any extensive property can be made intensive by dividing by the total mass, volume, or number. • SURROUNDINGS mostly just have a temperature. Later on you will learn that they can have other things, but for now, it is just T. • The symbols are T, V, p, M and m and N, E, H…
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6 Copyright: 2010 Prof. Magde Chapter 6: Energies in Reactions • According to the FIRST LAW, that energy is conserved, any change in the SYSTEM must have an equal but opposite change in the SURROUNDINGS. E sys =  E surr E is total energy. It is an extensive property A system has E. If the E sys increases, the added energy must come from the surroundings. The surroundings can transfer energy by two processes: by Q, heating (cooling), or by W, doing work. E sys = Q + W Heating increases random motion of atoms, either translational kinetic energy in gases, or rotational kinetic energy in gases, or vibrations, which are partly kinetic and partly potential energy of stretched springs in all states.
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6 Copyright: 2010 Prof. Magde Chapter 6: Enthalpy in Reactions • Chemists usually speak not of E itself, but of H,
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This note was uploaded on 01/12/2011 for the course CHEM 6A taught by Professor Pomeroy during the Fall '08 term at UCSD.

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Chapter6LEcture - Chapter 6: Energies in Reactions...

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