Chapter 14 - Equilibrium Many chemical reactions do not go...

Info iconThis preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Equilibrium Many chemical reactions do not go to completion, but rather reach a state where both reactants and products are present. In this situation we say that the system is at equilibrium . The equilibrium is characterized by an equilibrium constant. The reason that some reactions reach equilibrium and do not go to completion is a consequence of thermodynamics. The Nature of Equilibrium + 2 2 6 [ ( ) ] Co H O- 2 4 [ ( ) ] Co Cl + + 2 - 2- 2 6 4 2 [ ( ) ] 4Cl [CoCl ] + 6H O Co H O + + 2 - 2- 2 6 4 2 [ ( ) ] 4Cl [CoCl ] + 6H O Co H O 98% 2% The Approach to Equilibrium + 2 2 6 [ ( ) ] Co H O- 2 4 [ ( ) ] Co Cl + 2 2 6 [ ( ) ] Co H O 2 4 [ ( ) ] Co Cl Characteristics of Equilibrium 1. The system shows no macroscopic evidence of change. 2. Equilibrium is dynamic reactants are still being converted to products and products to reactants. + + 2 - 2- 2 6 4 2 [ ( ) ] 4Cl [CoCl ] + 6H O Co H O 3. The equilibrium state is independent of the direction of approach The Equilibrium Constant + + bB dD aA cC If we consider a generic system at equilibrium: Then we can define an equilibrium constant (K) such that: c d eq eq a eq eq [C] [D] = [A] [ ] ([A] - concentration of A at equilibrium) b eq K B No matter what the initial concentration of reactants is the value of K at equilibrium is always the same. This is the law of The Equilibrium Constant If the reaction is performed in the gas phase then we can replace the concentration ([ ]) units with partial pressures (remember for a gas the partial pressure is a direct measure of the number of gas phase molecules in a certain volume, which is a measure of concentration). c d C eq D eq a A eq A eq [P ] [P ] = [P ] [ ] ([P ] - partial pressure of A at equilibrium) b B eq K P In general, If K is large then the equilibrium concentration of the products is much larger than the reactants and the process is almost stoichiometric. If K is small then the equilibrium concentration of the products is much smaller than the reactants. If K is 1 then the equilibrium concentration of the products and reactants is similar. Examples of Equilibrium In the gas phase: + = 2 ( ) ( ) 2(g) 2 NO Cl 2 NOCl 2 2 Cl (P ) (P ) (P ) g g NOCl NO K In solution:- - + =- ( ) ( ) 3 (aq)- 2 - 3- 3 3 2 ClO [Cl ] [ClO ] [ClO ] aq aq ClO Cl K Concentration Values for Solids and Solvents Species (atoms, molecules etc.) in the solid phase do not contribute to a determination of the equilibrium constant. In other words [A (solid) ] = 1. The same is true for pure liquids or solvents; the most important example of this is for reactions performed in water ([H 2 O(l)] = 1)....
View Full Document

This note was uploaded on 01/20/2012 for the course CHEM 030.101 taught by Professor Draper during the Fall '08 term at Johns Hopkins.

Page1 / 44

Chapter 14 - Equilibrium Many chemical reactions do not go...

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online