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Chemistry Equilibrium

Chemistry Equilibrium. Equilibrium. Chemical equilibrium is a reaction state where both reactants and products are both present, but the concentrations of both are no longer changing. In other words, the forward reaction and the reverse reaction are occuring at the same rate.

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Chemistry Equilibrium

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  1. ChemistryEquilibrium

  2. Equilibrium • Chemical equilibrium is a reaction state where both reactants and products are both present, but the concentrations of both are no longer changing. • In other words, the forward reaction and the reverse reaction are occuring at the same rate. • Because of this, any reaction in equilibrium must be reversible. • Consider the decomposition of N2O4: • N2O4  2 NO2 • At equilibrium, the rate of the forward reaction, is equal to the rate of the reverse reaction.

  3. Equilibrium • A reaction may take some time to reach an equilibrium state – as the forward reaction starts quickly, the reverse reaction begins at a slow rate. • Eventually, the forward reaction rate equals the reverse reaction rate.

  4. Equilibrium Constants • The equilibrium constant is related to the rate laws of the forward and reverse reactions. • Given the generic reaction a A + b B  c C + d D • The concentration equilibrium constant, Keq, is equal to Keq = [C]c[D]d [A]a[B]b

  5. Equilibrium Conditions • There are three take home messages regarding equilibrium: • At equilibrium, the concentrations of reactants and products no longer change with time. • For equilibrium to occur, neither reactants nor products can escape from the system. • At equilibrium, a particular ratio of concentration terms equals a constant, known as the equilibrium constant (K).

  6. Keq Determination • What is Keq for the following reaction? N2 + 3 H2 2 NH3

  7. What is Keq for the reaction N2O4 2 NO2 ?

  8. Equilibrium Constant Magnitude Given the reaction CO(g) + Cl2 COCl2 Keq = 4.56 x 109 What is the Keq expression? • Because Keq is much larger than 1, at equilibrium, which are there more of: reactants or products?

  9. Equilibrium Constant Magnitude • If K >> 1, equilibrium lies “to the right” and products dominate. • If K << 1, equilibrium lies “to the left” and reactants dominate.

  10. Relating K and Reaction Direction • N2O4 2 NO2 Keq = 0.212What is Keq in the reverse direction? • Keq of the “forward reaction” is the reciprocal of the “reverse reaction” • Because it’s equilibrium, “forward” and “reverse” are arbitrary.

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