EquilibriumCh6-8

EquilibriumCh6-8 - Investigating Chemical Reactions N2O4...

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Unformatted text preview: Investigating Chemical Reactions N2O4 (g) 2 NO2 (g) Colorless brown Closed Container: Reversibility Groups of Molecules A state of Dynamic Equilibrium Equilibrium Concentrations Equilibrium is reached when the concentrations of products and reactants remains unchanged with time Condition dependent Qualitative descriptions Equilibrium lies to the left (or right) Equilibrium favors products (or reactants) Initial: all NO2 2 NO2 N2O4 Rates of Reaction For simple, one step reaction, reaction rate is due to inherent reactivity and collision rate Forward rate = kf [N2O4] Reverse rate = kr [NO2]2 Rates change over Course of Reaction Initial: all NO2 2 NO2 N2O4 Same Principle for all Reactions CO + H2O CO2 + H2 Law of Mass Balance General, Empirical Form: aA + bB cC + dD This is called the Equilibrium expression Law of Mass Balance Empirical lawwith justification from kinetics Example: N2O4 2 NO2 Forward rate = reverse rate This derivation is a simplification, but the outcome generally applies N2O4 (g) 2 NO2 (g) Keq = [NO2]2/[N2O4] If equilibrium [R] and [P] are known, Keq can be calculated. Example: at equilibrium, [NO2] = 1.50 x 10-2 M, [N2O4] = 1.03 x 10-2 M @ 317K (from experiment) Keq = (1.50 x 10-2)2/(1.03 x 10-2) = 0.0218 Keq depends on how the equation is written. N2O4 (g) 2 NO2 (g) K1 = [NO2]2/[N2O4] = 0.0218 2 NO2 (g) N2O4 (g) K2 = [N2O4] / [NO2]2 K2 = 1/K1 K2 = 1 / 0.0218 = 45.9 @ 317K N2O4 (g) NO2 (g) K3 = [NO2] /[N2O4]1/2 K3 = (K1)1/2 K3 = (0.0218)1/2 = 0.148 Small Keq (less than 1) means less product at equilibrium Large Keq (more than 1) means more product at equilibrium Test Your Understanding Calculate the equilibrium constant for at a given temperature if a 1-L container that initially held 1 mol of CO and 1 mol of water reached equilibrium and then had 0.13 mol of CO2 and H2. CO + H2O CO2 + H2 Answer: Keq = 0.022 Units? Keq describes ratio of reactants and products A B Keq =0.33 Which of the following systems are at equilibrium? [A] = 3.0 M, [B] = 1.0 M [A] = 7.5 x 10-3 M, [B] = 2.5 x 10-3 M [A] = 12.0 M, [B] = 4.0 M Keq describes ratio, not absolute concentrations Concentrations are dependent on starting point, Ratio of concentrations is not! Initial: all NO2 All proceed until equilibrium is reached One Equilibrium Constant, Many Equilibrium Positions all N2O4 both 2 NO2 N2O4 K1 = [N2O4] / [NO2]2 N2O4 + O2 2 NO3 K2 = [NO3]2 / [N2O4][O2] 2 NO2 + O2 2 NO3 K3 = [NO3]2 / [NO3]2 [O2] K3 = K1K2 Multiple Equilibria What if the products of one reaction act as reactants in a subsequent reaction?...
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This note was uploaded on 01/17/2012 for the course S 117 taught by Professor Stephenjacobson during the Fall '11 term at Indiana.

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EquilibriumCh6-8 - Investigating Chemical Reactions N2O4...

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