Chapter_15_Chemical_Equilibrium[1]

# Chapter_15_Chemical_Equilibrium[1] - Chapter 15 Chemical...

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Chapter 15 Chemical Equilibrium Chemical equilibrium – condition in which the concentrations of all reactants and products in a closed system cease to change. It occurs when opposing reactions are proceeding at equal rates. Examples include: vapor above a liquid, sodium chloride in water as the ions dispersed in water. 15.1 Concept of Equilibrium - For gases, we express equilibrium in partial pressures (atm) - For solutes in solution, we will use molarities When we look at the concept of equilibrium, we look at the reactions of: A B B A The first reaction is the forward reaction. The rate equation for it would be: Rate = k f [A] The second reaction is the reverse of that reaction. The rate equation for it would be: Rate = k r [B] We use ideal gas equation, we can convert to molarity. Performing further calculations, we can obtain a constant, k, from the calculations of: k f /k r = a constant We then can write the equilibrium equation as: A B 15.2 The Equilibrium Constant Law of Mass Action – expression of the relationship between the concentrations(expressed as partial pressures for gases and as molarities for solutions) of the reactants and products present at equilibrium in any reaction. aA + bB cC + dD

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K eq = P c c P d d /P a a P b b or for solutions K eq = [C] c [D] d /[A] a [B] b This is the equilibrium constant expression, or the equilibrium constant The K eq is products over reactants. The equilibrium constant expression depends only on the stoichiometry of the reaction, not on its mechanism. Magnitude of Equilibrium Constants
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Chapter_15_Chemical_Equilibrium[1] - Chapter 15 Chemical...

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