notes_Chapter 6 - Chapter 6: Chemical Equilibrium 6.1 The...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 6: Chemical Equilibrium 6.1 The Equilibrium Condition 6.2 The Equilibrium Constant 6.3 Equilibrium Expressions Involving Pressures 6.4 The Concept of Activity 6.5 Heterogeneous Equilibria 6.6 Applications of the Equilibrium Constant 6.7 Solving Equilibrium Problems 6.8 LeChatelier’s Principle Chemical Equilibrium • Previously, we assumed that a chemical reaction goes to completion as written. H 2 O( g ) + CO ( g ) ˠ H 2 (g) + CO 2 ( g ) • In general this is not correct. Instead, a stable state of the system in reached, which includes both reactants and products. It is called the equilibrium state, or simply “equilibrium”. H 2 O( g ) + CO ( g ) H 2 (g) + CO 2 ( g ) Molecular Picture of Establishment of Equilibrium CO( g ) + H 2 O( g ) CO 2 ( g ) + H 2 ( g ) INITIAL 7 CO( g ) + 7 H 2 O( g ) + 0 CO 2 ( g ) + 0 H 2 ( g ) AFTER IT STOPS CHANGING 2 CO( g ) + 2 H 2 O( g ) + 5 CO 2 ( g ) + 5 H 2 ( g ) Concentration vs. Time CO( g ) + H 2 O( g ) ˠ CO 2 ( g ) + H 2 ( g ) Ratio depends on temperature Characteristics of Chemical Equilibrium States Reaching equilibrium requires reactions to occur. Once reached, they show no macroscopic evidence of further change. Reached through dynamic balance of forward and reverse reaction rates . Forward rate = k 1 [NO 2 ][NO 2 ] = k 1 [NO 2 ] 2 Back rate = k -1 [NO 3 ][NO] k 1 and k -1 reflect probabilities that one collision leads to reaction Reverse: NO 3 (g) + NO(g) ˠ 2NO 2 (g) k -1 Equilibrium arises through dynamic balance between forward and back reactions
Background image of page 1

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

View Full DocumentRight Arrow Icon
Kinetics of Approach to Equilibrium At eqbm.: Forward rate = back rate k 1 NO 2 [] 2 = k 1 NO NO 3 [ ] k 1 k 1 = NO NO 3 NO 2 2 = K The Equilibrium Constant (K) Consider the generalized chemical reaction: a A + b B U c C + d D A, B, C and D represent chemical species and a, b, c , and d are their stoichiometric coefficients in the balanced chemical equation. At equilibrium, The square brackets indicate the concentrations of the species in equilibrium. K is a constant called the equilibrium constant. K depends only on T , and not on concentrations. Note: The “units” for K are concentration units raised to some power = c+d–(a+b) K = C [ ] c D [ ] d A a B b Equilibrium from Different Starting Points CO( g ) + 2 H 2 ( g ) CH 3 OH( g ) K = CH 3 OH CO H 2 2 All three species start from the same concentrations. N 2 ( g ) + 3 H 2 ( g ) U 2 NH 3 ( g ) Fe K = [NH 3 ] 2 [N 2 ][H 2 ] 3 Small K N 2 (g) + O 2 (g) U 2 NO (g) K = 1 x 10 –30 Essentially only reactants at equilibrium. Intermediate K 2 BrCl (g) U Br 2 (g) + Cl 2 (g) K = 5 Comparable amounts of products and reactants at equilibrium. Large K 2 CO (g) + O 2 (g) U 2 CO 2 (g) K = 2.2 x 10 22 Essentially only products atequilibrium. Equilibrium Constants Big and Small Equilibrium values can be wide ranging both big and small!!!
Background image of page 2
CS 2 ( g ) + 3 O 2 ( g ) U CO 2 ( g ) + 2 SO 2 ( g ) K 1 = CO 2 [] SO 2 [ ] 2 CS 2 O 2 3 K 2 = CS 2 O 2 3 CO 2 SO 2 2 = 1 K 1 The equilibrium expression for a reaction written in reverse is the reciprocal of that for the original expression.
Background image of page 3

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

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/06/2010 for the course CHEM 142 taught by Professor Iandearing during the Spring '10 term at University of Warsaw.

Page1 / 11

notes_Chapter 6 - Chapter 6: Chemical Equilibrium 6.1 The...

This preview shows document pages 1 - 4. Sign up to view the full document.

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