15 Chemical Equilibrium

15 Chemical Equilibrium - 15. Chemical Equilibrium 15.1....

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© David Hanson, Stony Brook University, 2008 Reproduction or distribution by any means is prohibited by law. 1 15. Chemical Equilibrium 15.1. What is meant by chemical equilibrium? A chemical reaction equation is written with the reactants on the left-hand side and the products on the right-hand side. For example, N 2 (g) + 3 H 2 (g) 2 NH 3 (g) (15.1.1) This equation clearly describes what happens if nitrogen and hydrogen gases are mixed. But what happens if some amount of pure ammonia, NH 3 , is placed in a container? Some of it will dissociate to produce nitrogen and ammonia! All chemical reaction equations really should be written with a double arrow. N 2 (g) + 3 H 2 (g) 2 NH 3 (g) (15.1.2) The double arrow signifies that an equilibrium is established between the concentrations of the reactants and the concentrations of the products. The reaction can go in either direction to establish this equilibrium. 15.2. Equilibrium Constant, K The equilibrium concentrations for reactants and products are determined by the equilibrium constant for that reaction at the specified temperature. The equilibrium constant for the generic reaction aA +bB cC + dD (15.2.1) is given by [ ] [ ] [ ] [ ] eq eq eq eq c d a b C D K A B (15.2.2) In the expression for the equilibrium constant, the symbol [A] eq represents the activity of reactant A at equilibrium. The activity is obtained from the concentration in moles/liter by dividing by the standard concentration, which is 1 mole/liter. When the activities at equilibrium are substituted into Eq. 15.2.2 the value of the
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This note was uploaded on 06/29/2008 for the course CHE 132 taught by Professor Hanson during the Spring '08 term at SUNY Stony Brook.

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15 Chemical Equilibrium - 15. Chemical Equilibrium 15.1....

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