Chem 112 Exam AID Course Pack

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Unformatted text preview: to : Ktotal=K1 K2 To solve equilibrium problems we use ICE tables where “I” refers to initial concentrations “C” refers to the changes that take place and “E” refers to the equilibrium concentrations composed of the initial concentrations and the changes that have occurred to establish equilibrium Occasionally we run into some problems and we must assume a reaction goes to completion and then do another ICE table with the reverse reaction to find equilibrium concentrations 10.0 Thermodynamics and Equilibrium € € Thermodynamics refers to a chemical reaction as a flow of atoms from reactants to products carried out at constant pressure and temperature Recall: ΔG<0 means the reaction is spontaneous in the forward direction and at equilibrium ΔG=0 • ΔG refers to the free energy available to do work (TΔS is the unavailable energy lost from the reaction in the form of heat Isothermal Processes (for reactions in the gas phase) Remember that if a pressure of an ideal gas is changed from P1 to P2 at constant T: 1) ΔG = ΔH − TΔS And the reaction is isothermal so ΔH=0 and therefore 2) ΔG = −TΔS And for an isothermal reaction entropy can be calculated solely from the partial pressures 3) ΔS = − nR ln And substituting equation three into equation two we get the complete equation: 4) ΔG = nRT ln € P2 P1 P2 ***note from before the pressure ratio is equal to K the equilibrium constant P1 And remember from before this equation: € Ethan Newton & Barry Zhang for SOS Winter 2012 44 ⎛ྎ [C ]c ⎞ྏ ⎟ྏ ΔG = ΔG o + RT ln⎜ྎ a b ⎟ྏ ⎜ྎ ⎝ྎ [A] [B] ⎠ྏ Example: For a chemical reaction involving gases is could be shown that for the following reaction: € These equations would be used to determine the free energy for a chemical reaction where the reactants and products are not in their standard states (note the use of activities by dividing by a reference pressure) • The standard state refers to a gas with a pressure of exactly 1 bar or a solution with a concentration of exactly 1M and when all components are in their standard states ΔG = ΔG o At equilibrium Involving solutions ΔG=0 and therefore ΔG° is calculated the same fashion as shown in the equilibrium € section; in total: ΔG = −RT ln K Where the K refers to KC Similarly if th...
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