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CHEM 112 Winter Study Guide.docx

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Queen's University
CHEM 112

CHEM 112 Winter Study Guide Physical and Chemical Equilibrium Related Formulae ∆G rxnT ln ⁡(K) g h aA+bB↔≫+hH K = [G] [H] For the reaction as follows: , c [A] [B] b 2 (PSO3) For the reaction in gas phase, 2SO (2)+O (g2↔2SO (g) 3 , K p 2 (P SO2 (PO)2 P = [X ]RT and thus K =K (RT) ∆n x P c Definitions ∆G ° is the change in Gibb’s free [ ] is the concentration in mol/L rxn energy P is the partial pressure R is the ideal gas law constant, 8.314 K is the equilibrium constant J ∆n is the stoichiometric difference between products and reactants mol∗° K T is the temperature in Kelvins Key Concepts Equilibrium Achemical equilibrium displays all of the following characteristics: • The system is closed • The system shows no macroscopic evidence of change • Equilibrium is reached through a spontaneous reaction • Adynamic balance of forward and reverse reactions exists • When temperature is constant, the same equilibrium constant will be obtained, regardless of the direction from which it was approached When K is large, almost 100% of limiting reagent is consumed and thus the reaction is considered to go to completion. Similarly, when K is very small, the reaction is considered not go at all. Types of Equilibrium Systems • Homogenous gas phase systems • Heterogenous mixtures of solid/gas, solid/aqueous, aqueous/gas • Reactions involving substances such as acid/base reactions or redox reactions Relationship of ‘K’ to the Balanced Chemical Reaction • Inverting the BCE causes inversion of K • Multiplying by coefficients by a common factor raises K to that common factor • Dividing coefficients by a common factor causes K to be taken to that factor’s root Le Châtelier’s Principle When an equilibrium system is subjected to a change in temperature, pressure or concentration of reacting species, the system responds by attaining a new equilibrium that partially offsets the impact of the change. • Raising the temperature of the reaction causes the reaction to shift in direction of the endothermic reaction to consume the heat energy • Lowering the temperature of the reaction causes the reaction to shift in the direction of the exothermic reaction to produce the lost energy Example Consider the system as follows: H 2I 22 HI −2 −2 H Amixture contains 2.0 x 10 mol of HI, 1.0 x 10 mol of 2 , and 3.0 x 10−2 mol of I2 in a 2.0L container at 721 K. The equilibrium constant is K =50.5 for this system at 712 K. c 1. Is this system at equilibrium? [HI ] (2.0x 10 mol/2.0 L) 2 Q c ❑= −2 −2 =1.33 [H 2[I2] (1.0 x10 mol/2.0 L)(3.0 x10 mol/2.0 L) Since Q
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