1 / 21

Ch 18: Chemical Equilibrium

Ch 18: Chemical Equilibrium. Section 18.2 Shifting Equilibrium. Reversible Reactions. Reversible Reactions : one in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously. The double arrow tells you that the reaction is reversible.

samuelbell
Download Presentation

Ch 18: Chemical Equilibrium

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ch 18: Chemical Equilibrium

  2. Section 18.2Shifting Equilibrium

  3. Reversible Reactions • Reversible Reactions: one in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously. • The double arrow tells you that the reaction is reversible. 2 SO2(g) + O2(g) ⇄ 2 SO3(g)

  4. Chemical Equilibrium: when the rates of the forward and reverse reactions are equal, the reaction has reached a state of balance. • At chemical equilibrium, no net change occurs in the actual amounts of the components of the system. • The relative concentrations of the reactants and products at equilibrium constitute the equilibrium position of a reaction.

  5. Think of a 2-story mall with an escalator. You have 100 people on the top floor and 50 people on the bottom floor. If 10 people want to move to the top floor, how can this happen while still keeping 100 people on the top and 50 people on the bottom? • You will have to have 10 people go down the escalator at the same time as 10 people go up the escalator. • People are moving at the same RATE!

  6. Factors Affecting Equilibrium: Le Châtelier’s Principle • Le Châtelier’s Principle: If a stress is applied to a system in dynamic equilibrium, the system changes in a way that relieves the stress. • There are three factors that we will talk about that can affect equilibrium.

  7. CONCENTRATION • If you add more of a reactant, the reaction goes toward the products. • If you take away some of a reactant, the reaction goes toward the reactants. • If you add more of a product, the reaction goes toward the reactants. • If you take away some of a product, the reaction goes toward the products.

  8. TEMPERATURE • If heat is a product and you add heat, the reaction shifts toward the reactants. • If heat is a reactant and you add heat, the reaction shifts toward the products. • If heat is a product and you take away heat, the reaction shifts toward the products. • If heat is a reactant and you take away heat, the reaction shifts toward the reactants.

  9. PRESSURE – ONLY GASES!! • If you increase pressure, the reaction shifts towards the side with less moles. • If you decrease pressure, the reaction shifts towards the side with more moles.

  10. VOLUME – ONLY GASES!! • If you ­­­­­­­­­­­­increase volume, it is the same as decreasing pressure, so the reaction shifts towards the side with more moles. • If you ­­­­­­­­­­­­decrease volume, it is the same as increasing pressure, so the reaction shifts towards the side with less moles. • Because it is the same as changing pressure, we do not consider this to be a 4th factor.

  11. CATALYSTS • Adding a catalyst has no effect on the equilibrium, it will only help to reach equilibrium faster.

  12. Reactions to Completion • A reaction is considered to “go to completion”, when almost all of the ions are removed from the solution. • This depends on the solubility of the product formed, and if it is soluble, then on its degree of ionization.

  13. Formation of a Gas • Gases are not very soluble, so when a gas is formed and the reaction container is open to the air, the gas will escape and the reaction will go almost to completion.

  14. Formation of a Slightly Ionized Product • This occurs with the neutralization reactions of acids and bases. • HCl(aq) + NaOH(aq) • H3O+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) Na+(aq) + Cl-(aq) + 2H2O(l) • H3O+(aq) + OH-(aq) 2H2O(l) • Water only slightly ionizes, so it exists as mainly H2O molecules.

  15. Formation of a Precipitate • If a product is insoluble (a precipitate), then when the product forms, it cannot dissolve to allow the reaction to go in the reverse direction. • NaCl(aq) + AgNO3(aq) NaNO3(aq) + AgCl(s)

  16. Section 18.1 The Nature of Chemical Equilibrium

  17. Equilibrium Expressions • Equilibrium Constant: Keq is the ratio of product concentrations to reactant concentrations at equilibrium. nA + mB ⇄ xC + yD Keq = [C]x [D]y [A]n [B]m

  18. Write Equilibrium Expressions: • H2 + I2↔ 2HI • 2HgO ↔ 2Hg + O2 • 2SO2 + O2↔ 2SO3 • N2 + 3H2↔ 2NH3

  19. Equilibrium Constants • To find an Equilibrium Constant, plug in the concentrations of the reactants and products into the equilibrium expression and solve! • Keq> 1, products favored at equilibrium • Keq < 1, reactants favored at equilibrium • Keq does not have any units.

  20. CALCULATING Keq • A liter of a gas mixture at equilibrium at 10°C contains 0.0045 mol of N2O4 and 0.030 mol of NO2. Write the expression for the equilibrium constant and calculate Keq. N2O4(g) ⇄ 2NO2(g) Keq = [NO2]2 = (0.030 mol/L)2 [N2O4] = 0.0045 mol/L Keq = 0.20

  21. CALCULATING Keq • An equilibrium mixture of N2, O2, and NO gases is determined to consist of 6.4 mol/L of N2, 1.7 mol/L of O2, and 1.1 mol/L of NO. What is the Keqfor this system? N2 + O2⇄ 2NO Keq = [NO]2 [N2] x [O2] Keq = (1.1)2 (6.4) x (1.7) Keq = 0.11

More Related