Download Survey of Chemistry I - Chemical Equilibrium - Slides | CHEM 1151K and more Study notes Chemistry in PDF only on Docsity! 1 Chapter 9 Chemical Equilibrium 9.3 Equilibrium Constants General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 2 Equilibrium Constants For the reaction aA bB The equilibrium constant expression, Kc, gives the concentrations of the reactants and products at equilibrium: Kc = [B]b = [Products] [A]a [Reactants] The square brackets indicate the moles/liter of each substance. The coefficients b and a are written as superscripts that raise the moles/liter to a specific power. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 5 Learning Check Which of the following is the correctly written Kc expression for the reaction shown below? N2(g) + 3Cl2(g) 2NCl3(g) 1) [NCl3] 2) [N2][Cl2]3 [N2][Cl2] [NCl3]2 3) [NCl3]2 4) [NCl3]2 [N2]3 [Cl2] [N2][Cl2]3 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 6 Solution STEP 1 Write the balanced equilibrium equation: N2(g) + 3Cl2(g) 2NCl3(g) STEP 2 Write the product concentrations in the numerator and the reactant concentration in the denominator: Kc = [NCl3] [products] [N2][Cl2] [reactants] STEP 3 Write the coefficients as superscripts. Kc = [NCl3]2 (4) [N2][Cl2]3 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 7 Heterogeneous Equilibrium In heterogeneous equilibrium, Gases and solid and/or liquid states are part of the reaction. 2NaHCO3(s) Na2CO3(s) + CO2(g) + H2O(g) The concentration of solids and liquids is constant. The Kc expression is written with only the compounds that are gases. Kc = [CO2][H2O] General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. Guide to Calculating the Kc Value 10General, Organic, and Biological Chemistry 11 Example of Calculating Equilibrium Constants What is the Kc for the following reaction? H2(g) + I2(g) 2HI(g) Equilibrium concentrations: [H2] = 1.2 moles/L [I2] = 1.2 moles/L [HI] = 0.35 mole/L STEP 1 Write the Kc expression: Kc = [HI]2 [H2][I2] STEP 2 Substitute the equilibrium concentrations in Kc: Kc = [0.35]2 = 8.5 x 10-2 [1.2][1.2] General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 12 Learning Check Calculate the Kc for the following reaction: CH4(g) + H2O(g) CO(g) + 3H2(g) with the following equilibrium concentrations: [CH4] = 0.13 M [H2O] = 0.53 M [CO] = 0.81 M [H2] = 0.28 M 1) 0.26 2) 3.3 3) 3.9 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.
