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Reversible Reactions: Understanding Equilibrium in Chemistry

Learn about reversible reactions, equilibrium in chemical systems, and factors affecting equilibrium using Le Châtelier's Principle. Explore how concentrations, temperature, and pressure impact the equilibrium position.

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Reversible Reactions: Understanding Equilibrium in Chemistry

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  1. Chemistry 18.2

  2. Check answers for SA 18.1 • The rate of a chemical reaction is the amount of reactant changing per unit of time. • Temperature, concentration, particle size, use of a catalyst • No; the collision must have sufficient energy to break and form bonds. • No; the collision must have sufficient energy to break and form bonds.

  3. 18.2 Reversible Reactions • Reversible Reactions • How do the amounts of reactants and products change in a chemical system at equilibrium? • What do you think??

  4. 18.2 Reversible Reactions • At chemical equilibrium, no net change occurs in the actual amounts of the components of the system.

  5. 18.2 Reversible Reactions • Example: • If the rate of the shoppers going up the escalator is equal to the rate of the shoppers going down, then the number of shoppers on each floor remains constant, and there is an equilibrium.

  6. 18.2 Reversible Reactions • A reversible reaction is one in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously.

  7. 18.2 Reversible Reactions SO3 decomposes to SO2 and O2 SO2 and O2 react to give SO3 At equilibrium, all three types of molecules are present.

  8. 18.2 Reversible Reactions • When the rates of the forward and reverse reactions are equal, the reaction has reached a state of balance called chemical equilibrium. • The relative concentrations of the reactants and products at equilibrium constitute the equilibrium position of a reaction.

  9. 18.2 Reversible Reactions

  10. 18.2 Factors Affecting Equilibrium: Le Châtelier’s Principle • Factors Affecting Equilibrium: Le Châtelier’s Principle • What three stresses can cause a change in the equilibrium position of a chemical system?

  11. 18.2 Factors Affecting Equilibrium: Le Châtelier’s Principle • Stresses that upset the equilibrium of a chemical system include changes in the concentration of reactants or products, changes in temperature, and changes in pressure.

  12. 18.2 Factors Affecting Equilibrium: Le Châtelier’s Principle • The French chemist Le Châtelier proposed what has come to be called • 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.

  13. 18.2 Factors Affecting Equilibrium: Le Châtelier’s Principle • Concentration • Rapid breathing during and after vigorous exercise helps reestablish the body’s correct CO2:H2CO3 equilibrium, keeping the acid concentration in the blood within a safe range.

  14. 18.2 Factors Affecting Equilibrium: Le Châtelier’s Principle • Temperature • Dinitrogen tetroxide is a colorless gas; nitrogen dioxide is a brown gas. The flask on the left is in a dish of hot water; the flask on the right is in ice.

  15. 18.2 Factors Affecting Equilibrium: Le Châtelier’s Principle • Pressure • Pressure affects a mixture of nitrogen, hydrogen, and ammonia at equilibrium

  16. Conceptual Problem 18.1

  17. Conceptual Problem 18.1

  18. Conceptual Problem 18.1

  19. for Conceptual Problem 18.1 Problem Solving 18.6 Solve a similar problem with the help of an interactive guided tutorial.

  20. 18.2 Equilibrium Constants • The equilibrium constant (Keq) is the ratio of product concentrations to reactant concentrations at equilibrium. • Exponents = Coefficients

  21. 18.2 Equilibrium Constants • Size shows whether R or P are favored. • Keq > 1 means products are favored • Keq < 1 means reactants are favored

  22. 18.1

  23. 18.1

  24. 18.1

  25. 18.1

  26. 18.2 • SA 18.2: 1-2, 4, 6-8, 11-13, 16

  27. 18.2 Section Quiz. • 18.2.

  28. 18.2 Section Quiz. • 1. In a reaction at equilibrium, reactants and products • decrease in concentration. • form at equal rates. • have equal concentrations. • have stopped reacting.

  29. 18.2 Section Quiz. • 2. In the reaction 2NO2(g)  2NO(g) + O2(g), increasing the pressure on the reaction would cause • the amount of NO to increase. • the amount of NO2 to increase. • nothing to happen. • the amount of O2 to increase.

  30. 18.2 Section Quiz. • 3. Changing which of the following would NOT affect the equilibrium position of a chemical reaction? • concentration of a reactant only • concentration of a product only • temperature only • volume only

  31. 18.2 Section Quiz. • 4. For the following reaction, Keq = 1. • A(g) + B(g)  C(g) + D(g) Therefore, at equilibrium • [C] = [A]. • [A][B] = 0. • [AB] = [CD] = 1. • [A][B] = [C][D].

  32. END OF SHOW

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