Chemical Equilibrium Chapter 18B West Valley High School General Chemistry Mr. Mata Copyright©2000 by Houghton Mifflin Company. All rights reserved.

The Equilibrium Expression nA + mB <-> xC + yD A & B = reactants; C & D = products n, m, x, & y = coefficients A + B -> C + D (forward reaction) A + B <- C + D (reverse reaction) Equilibrium: forward rate = reverse rate Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Predicting Equilibrium Shift Changes in Pressure: N2 + 3H2 <-> 2NH3 Initial: 4 moles reactant : 2 moles product Action: Increase pressure on system. Result: equilibrium shift to right (product). Why: increasing pressure on reactant (more moles) causes shift to product (fewer moles). Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Predicting Equilibrium Shift Changes in Concentration: A + B <-> C + D Initial: system in equilibrium Action: Increase concentration of A. Result: equilibrium shift to right (product). Why: Increase reactant [A] causes decrease in reactant [B] -> more C & D produced. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Predicting Equilibrium Shift Changes in Concentration: A + B <-> C + D Initial: system in equilibrium Action: Increase concentration of D. Result: equilibrium shift to left (reactant). Why: Increase product D conc causes decrease in product C conc -> more A & B reactants. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Predicting Equilibrium Shift Changes in Temperature: N2 + 3H2 <-> 2NH3 Initial: system in equilibrium Action: Increase temperature on system. Result: equilibrium shift to right (product). Why: Increasing temp adds energy in the form of heat (endothermic; reactant); System shifts to right (product). Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Completion Reactions Rxns that convert all reactants to products. Evidence for completion reactions: Formation of a gas Ex: gas escapes to open air Formation of a precipitate (ppt.) Ex: insoluble solid product is formed Neutralization reaction Ex: salt & water are products in reaction Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Equilibrium Constant Expression Use an equilibrium constant, Keq Abbreviated definition is Keq = [products] [reactants] Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Equilibrium Constants aA + bB  cC + dD Keq = [ C ]c [ D ]d [ A ]a [ B ]b [ ] = concentration in moles/liter (M) a, b, c, d = coefficients A, B = reactants; C, D = products Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Equilibrium Problem #1 If the concentration of nitrogen is 6M, the concentration of hydrogen is 3M, and the concentration of ammonia is 2M, what is the Keq value for this reaction? __ N2 + __ H2 <-> __ NH3 Solve: Balance chemical equation 1 N2 + 3 H2 -> 2 NH3 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Equilibrium Problem #1 Knowns: [N2] = 6M, [H2] = 3M, [NH3] = 2M Unknown: Keq = ? Keq = [products] = [NH3]2 [reactants] [N2] [H2]3 Keq = [2M]2 = 0.02 [6M] [3M]3 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Equilibrium Problem #2 Calculate the Keq for this reaction if concentration of hydrogen is 2M, concentration of hydrogen iodide is 6M, and the concentration of iodine is 12M. __ H2 + __ I2 <-> __ HI Solve: Balance chemical equation 1 H2 + 1 I2 -> 2 HI Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Equilibrium Problem #2 Knowns: [H2] = 2M, [I2] = 12M, [HI] = 6M Unknown: Keq = ? Keq = [products] = [HI]2 [reactants] [H2] [I2] Keq = [6M]2 = 1.5 [2M] [12M] Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Meaning of Equilibrium Constant Keq Use letter K to represent the CONSTANT Calculate a numerical value (no units) If Keq < 1, reactants favored; shift to left (little product made) If Keq > 1, products favored; shift to right (good way to manufacture product)

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Chapter 18 SUTW Prompt Describe how pressure, concentration, and temperature can cause equilibrium to shift in a chemical equation. Complete a 11 -12 sentence paragraph using the SUTW paragraph format. Hilight using green, yellow, and pink. Due Date: Tuesday, February 27, 2017 (start of class). Copyright©2000 by Houghton Mifflin Company. All rights reserved.