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Unformatted text preview: Chem 6B Equation Sheet (Exam 1) 1 Prof. Crowell Chem 6B Exam 1 Equation Sheet 1 st Law : the total amount of energy in the universe is constant (energy is conserved). U q w = + = + = + = + 2 nd Law : in any spontaneous change the entropy of the universe increases. universe S > > > > 3 rd Law : the entropy of any pure, perfect crystalline solid at absolute zero is zero. system S at K = ! State Function : - a physical property like U, H, T, V, P that has a specific value once the state is defined; it depends only on the state of the system and not the pathway. Extensive Variables :- properties that depend upon the amount (mass) or extent of the sample (e.g. M, n, V, C, U, S, G, etc.). Intensive Variables :- properties that depend upon the nature but not on the amount (e.g. T, P, , = M/V, i = n i /n, V/n, U/n, S/n, H/n, G/n, etc.). An open system can exchange both matter & energy with its surroundings. A closed system can exchange energy with the surroundings but not matter. An isolated system cannot exchange energy nor matter. Diathermic Walls allow energy to flow as heat if there is a temperature difference between the system & surroundings, whereas Adiabatic Walls do not allow heat to flow even if there is a T difference. Reversible Process A process involving a series of infinitesimal changes . At each step in a reversible process, the system is in mechanical equilibrium with its surroundings. Irreversible Process A process in which change occurs by finite amounts. With finite steps, the system is not in mechanical equilibrium (e.g. P or T) with its surroundings during each step in the process. The work done in the expansion process approaches the reversible process as the number of steps becomes larger. The maximum work that can be done in an expansion is during a reversible process. Work is the energy transferred between a system and its surroundings as a result of unbalanced forces between the two, such as when an object is moved by a force. work = force x distance = N-m = kg-m 2 /s 2 = J, Expansion work = - P ex V = Pa-m 3 = J U = internal energy = KE + PE = system capacity to do work = total energy storage of a system Sign convention is viewed from the perspective of the system : Heat and work are both positive when they enter the system, and are both negative when they leave the system. Ideal gas law: First law of thermodynamics: Expansion work against a constant external pressure: Work of reversible, isothermal expansion of an ideal gas: ln ext final init PV nRT U q w w P V V w n R T V = = + = = + = = + = = + = = = = = = = = Isothermal Constant Temperature with corresponding changes in Pressure , Volume , and with Heat added or removed....
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This note was uploaded on 04/07/2008 for the course CHEM 6B taught by Professor Crowell during the Winter '08 term at UCSD.
- Winter '08