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Chapter 15 Chemical Equilibrium

Chapter 15 Chemical Equilibrium. BLB 12 th. 2 NO 2 (g) → 2 NO(g) + O 2 (g). ⇌. N 2 O 4 ( g ) colorless. 2 NO 2 ( g ) brown. 15.1 The Concept of Equilibrium. Chemical equilibrium occurs when a reaction and its reverse reaction proceed at the same rate. ⇌. N 2 O 4 ( g ). 2 NO 2 ( g ).

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Chapter 15 Chemical Equilibrium

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  1. Chapter 15Chemical Equilibrium BLB 12th

  2. 2 NO2(g) → 2 NO(g) + O2(g)

  3. ⇌ N2O4(g) colorless 2 NO2(g) brown 15.1 The Concept of Equilibrium Chemical equilibrium occurs when a reaction and its reverse reaction proceed at the same rate.

  4. ⇌ N2O4(g) 2 NO2(g) The Concept of Equilibrium • As a system approaches equilibrium, both the forward and reverse reactions are occurring. • At equilibrium, the forward and reverse reactions are proceeding at the same rate.

  5. ⇌ N2O4(g) 2 NO2(g) A System at Equilibrium • Once equilibrium is achieved, the concen-trations of reactants and products remain constant. • Ratio of concentration values equals a constant.

  6. The Concept of Equilibrium • The reaction system is closed. • Opposing reactions occur at equal rates, that is, the rates of forward and reverse reactions are equal. • Dynamic process (never stops) • Concentrations of reactants and products are constant. • Equilibrium can be reached from either direction, reactants or products.

  7. 15.2 The Equilibrium Constant aA + bB ⇌ cC + dD

  8. 15.2 The Equilibrium Constant • Kis constant for a reaction, regardless of the [A]0. • K is temperature dependent. • K depends on stoichiometry, not on the mechanism. • Pure solid or liquid reactant & products are not included for heterogeneous equilibria. (15.4, p. 623) • Water (or other pure solvent) is not included if the reactant and product concentrations are low. (p. 625) • Kc – concentrations (M) of solutions • Kp – partial pressures of gases; p. 617 to convert betweenKp &Kc

  9. Write the expression for K. • N2(g) +O2(g) ⇌ 2 NO(g) • 2 SO2(g) + O2(g) ⇌ 2 SO3(g)

  10. ⇌ N2O4(g) 2 NO2(g) Evaluating K

  11. 15.3 Understanding and Working with Equilibrium Constants The Magnitude of K • K >> 1 Essentially all products; lies to right K > 1 product-favored K < 1 reactant-favored K << 1 Essentially all reactants; lies to left

  12. Manipulating K (pp. 620-622) • Reverse reaction: • Adding reactions: • Multiplying reaction by some factor: #1: C(s) + ½ O2(g) ⇌ CO(g) #2: 2 C(s) + O2(g) ⇌ 2 CO(g)

  13. 15.4 Heterogeneous Equilibria • Reactant components are in different phases. • When a pure solid or liquid is involved in a heterogeneous equilibrium, its concentration is not included in the K expression. • The concentration of a pure solid or pure liquid doesn’t change. • Write the K expression: SnO2(s) +2 CO(g) ⇌ Sn(s) + 2 CO2(g)

  14. 15.5 Calculating Equilibrium Constants • Must plug in the equilibrium concentrations of reactants and products • A concentration table with initial, change, and equilibrium concentrations is set up. • See Sample Exercise 15.9. • More in lab and in Chapter 16 with weak acids and bases.

  15. Calculating K N2(g) + 3 H2(g) ⇌ 2 NH3(g) p. 642 @ 472°C 2.46 7.38 0.166 ← eq. partial pressures (atm)

  16. 15.6 Applications of Equilibrium Constants • Predicting the direction a reaction must proceed to establish equilibrium • The reaction quotient, Q (p. 627) • Q has the same form as K, but for non-equilibrium conditions. • Comparing Q and K: Q < K achieves equilibrium by shifting to right Q = K @ equilibrium Q > K achieves equilibrium by shifting to left

  17. Sample problem 46a N2(g) + 3 H2(g) ⇌ 2 NH3(g) KP= 4.51 x 10-5 at 450°C 45 atm55 atm 98 atm

  18. 15.7 Le Châtelier’s Principle If a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, the system will shift its equilibrium position to counter the effect of the disturbance. (p. 631)

  19. N2(g) + 3 H2(g) ⇌ 2 NH3(g)

  20. Le Châtelier’s Principle

  21. ⇌ N2O4(g) 2 NO2(g)

  22. ⇌ N2O4(g) colorless 2 NO2(g) brown 15.1 The Concept of Equilibrium Chemical equilibrium occurs when a reaction and its reverse reaction proceed at the same rate.

  23. Sample problem 61 2 SO2(g) + O2(g) ⇌ 2 SO3(g) ΔH < 0 Effect on equilibrium mixture when… (a) O2(g) is added? (b) the reaction mixture is heated? (c) the volume of container is doubled? (d) a catalyst is added? (e) the total P is increased by adding a noble gas? (f) SO3(g) is removed?

  24. 6 CO2(g) + 6 H2O(l) ⇌ C6H12O6(s) + 6 O2(g) ΔH = 2816 kJ Write the K expression. Effect on equilibrium mixture when… (a) PCO2 is increased? (b) the reaction is heated? (c) some CO2(g) is removed? (d) the total P is decreased? (e) part of C6H12O6(s) is removed? (f) a catalyst is added?

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