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Chemical Equilibrium

Chemical Equilibrium. Chemistry. Ms. Siddall. Reversible Reactions. Standard 9b: equilibrium conditions. Most reactions are ‘reversible’ Forward reaction : reactants make products e.x. 3O 2(g)  2O 3(g) Reverse reaction : products make reactants e.x. 2O 3(g)  3O 2(g)

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Chemical Equilibrium

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  1. Chemical Equilibrium Chemistry. Ms. Siddall

  2. Reversible Reactions Standard 9b: equilibrium conditions • Most reactions are ‘reversible’ • Forward reaction: reactants make products e.x. 3O2(g)  2O3(g) • Reverse reaction: products make reactants e.x. 2O3(g)  3O2(g) • In a reversible reaction the forward and reverse reactions occur at the same time e.x. 3O2(g) 2 O3(g)

  3. Summary 1 • What is a reversible reaction?

  4. Reversible reactions reach equilibrium: a balance between reactants and products Conditions of Equilibrium: • rate of forward reaction = rate of reverse reaction • Concentration of reactants and products is constant (does not change) NOTE: Rate = speed Concentration = number of particles or moles example: [HCl] = concentration of HCl 6M HCl = 6mole/L HCl = 6 moles of HCl per liter of solution

  5. Summary 2 • What is equilibrium?

  6. Reversible reaction: X  Y [X] X  Y concentration rate [Y] Y  X time time Concentrations are constant Reaction rates are equal equilibrium

  7. Summary 3 • Describe the part of each graph that illustrates equilibrium conditions.

  8. 9a: Le Chatelier’s Principle Le Chatelier’s Principle • A system in equilibrium will react to relieve stress (change) and re-establish equilibrium • Stress: • Adding reactants or products • Removing reactants or products • Changing temperature • Changing pressure (for gases only)

  9. Summary 4 • According to Le Chatelier’s Principle, what will happen to a system at equilibrium if more reactants or products are added?

  10. Example: N2(g) + 3H2(g) 2NH3(g) + heat • Stress: Add N2 • Stress relief: • Forward reaction (→) to get rid of N2 • H2 is used up (↓) • NH3 and Heat are produced (↑)

  11. Summary 5: N2(g) + 3H2(g) 2NH3(g) + heat • Stress: remove N2 • Stress relief: • Which way does equilibrium shift? • What happens to [H2]? • What happens to [NH3]? • What happens to heat?

  12. Stress relief. • Adding products or reactants • Equilibrium shifts to remove addition • Removing products or reactants • Equilibrium shifts to replace what has been removed • Gasses • Equilibrium shifts to produce: • more gas at low pressure • Less gas at high pressure

  13. Summary 6 • Why would a gas equilibrium system produce more gas at low pressure and less gas at high pressure?

  14. Haber Process: N2(g) + 3H2(g) 2NH3(g) + heat

  15. Haber Process: N2(g) + 3H2(g) 2NH3(g) + heat

  16. Summary 7 • According to Le Chatelier’s Principle: • Increasing reactant concentration will cause: • other reactants to __________? • products to __________? • Decreasing reactant concentration will cause: • other reactants to __________? • products to __________?

  17. A(g) + B(g) AB(g) + heat

  18. Summary 8 A(g) + B(g) AB(g) + heat • Complete the table of equilibrium changes

  19. A(g) + B(g) AB(g) + heat

  20. A(g) + B(g) AB(g) + heat

  21. Equilibrium Constant: Keq HONORS Standard 9c: equilibrium constant • At equilibrium concentrations are constant • Keq represents concentrations of reactants and products at equilibrium • Example: aA + bB  cC + dD • Keq = [C]c[D]d [A]a[B]b

  22. Summary 9 • write Keq expression for the Haber-Bosch Process: N2(g) + 3H2(g) 2NH3(g)

  23. Concentrations calculated in mol/L (M) • Only solutions(aq) & gases(g) are considered • No solids (s) • No liquids (l) Example: 2H2O(l) 2H2(g) + O2(g) Keq = [H2]2[O2]

  24. Summary 10 • Fe(OH)2(aq) + 2HSO3(aq)Fe(SO3)2(aq) + 2H2O(l) • Find Keq

  25. What Keq tells us • If Keq ≤ 1 There are more reactants than products at equilibrium • If Keq ≤ 1/100 There are mostly reactants at equilibrium • If Keq ≥ 1 There are more products than reactants at equilibrium • If Keq ≥ 100 There are mostly products at equilibrium

  26. Summary 11 CO(g) + 2H2(g) CH3OH(g) Keq=290 at 430°C • Write the expression for Keq • Reaction is… (mostly products or reactants?)

  27. Solubility • Ksp is the equilibrium constant for solubility • Example: AgCl(s) Ag+(aq) + Cl-(aq) • Ksp AgCl = 1.77 x 10-10 • Does not really dissolve, mostly solid • Example: AgNO3(s) Ag+(aq) + NO3-(aq) • Ksp AgNO3~ 1 x 1010 • Very soluble

  28. Summary 13 • Write the balanced equation for the dissolving of sodium sulfate. • Write a Ksp expression for the reaction.

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