chapt20_F110 - Overview Gas Lawsunits, laws, etc. Kinetic

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1 Overview Gas Laws—units, laws, etc. Kinetic Theory—atomic/molecular scale, counting molecules, counting collisions, etc. Chemical Kinetics 1. experimental measurements 2. mechanism or theory of reaction processes Thermodynamics 1. the first law—thermochemistry 2. the second law—entropy, equilibrium, spontaneity 3. the third law—entropy at 0 K, physical and chemical limits 4. phase equilibrium Chapter 20 Newton’s laws F=ma F=force in newtons m=mass in kg a = acceleration in m/s 2 dx dE F p = where E p =potential energy Examples of potential energy (stored energy, “energy of position”) Hook’s law: E p = ½ k x 2 k=force constant x=spring extension The force here: F = - k x Gravity: E p = mgh m=mass g=9.8 m/s 2 h=height The force here: F = - m g Thus potential energy can be associated with force. Kinetic Energy (energy associated with motion) E k = ½ m u 2 m=mass u=speed Force and energy are different. Units Energy units: 2 2 1 1 s m kg J = Force units: 2 1 1 s m kg N = The challenge is to see how mechanical systems (springs, falling bodies, etc.) exchange potential and kinetic energy. And what does this have to do with chemistry? Chemical systems store energy. But a more important issue is spontaneity. A spontaneous process is NOT necessarily exothermic. (examples?)
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2 Work: = dl F W W is the work, F is a force, and dl is distance Note the vector notation here. Direction is very important. If F is constant, then θ cos = L F W L is the distance through which the force F is applied and the vectors F and L make an angle θ with respect to one another. Note: the units of work are, N m which must be the same as a J. Work in terms of gases Energy FLOW If P2 > P1, E flows from the surroundings into the system, the Gas. Endothermic Δ E = E f - E i > 0 If P2 < P1, E flows from the system into the surroundings Exothermic Δ E = E f - E i < 0 If P1 and P2 are not near each other in value, a process will take place spontaneously, either an expansion (P1 > P2) or a compression (P1 < P2) Units of pressure, P: 2 2 2 2 s m kg m s m kg m N A F P = = = Here F means force, A means area, N stands for Newton, m is meters, kg is kilograms, and s is seconds. This unit of pressure, the Newton per meter squared is also called a Pascal, Pa 2 1 1 m N Pa = The units of work for an expanding gas must be J again. This is PV (show this!!) Types of systems: Open—allows mass to flow in and out of the system Closed—allows only energy to flow in and out of the sytem (either work or heat) Isolated—allows NO mass and NO energy to flow between system and surroundings. Gas Laws for closed systems: Gas, P1 Atmospheric Pressure, P2
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3 Boyle—pressure and volume are inversely related at constant temperature Charles—temperature and volume are directly related at constant pressure Amonton—temperature and pressure are directly related at constant volume But the law that can take the place of all three laws is the Ideal Gas Law:
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This note was uploaded on 09/11/2011 for the course CHEMISTRY 3441 taught by Professor Lobue during the Spring '11 term at Georgia Southern University .

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chapt20_F110 - Overview Gas Lawsunits, laws, etc. Kinetic

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