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Equilibrium

Equilibrium. Chemical Equilibrium Review. Most chemical reactions do not go to completion. They appear to stop. • These reactions are reversible A chemical reaction that can occur in both the forward and reverse direction. Chemical Equilibrium.

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Equilibrium

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  1. Equilibrium

  2. Chemical Equilibrium Review • Most chemical reactions do not go to completion. They appear to stop. • These reactions are reversible • A chemical reaction that can occur in both the forward and reverse direction

  3. Chemical Equilibrium • A state in which the forward and reverse reactions balance each other because they take place at equal rates. Rate forward reaction = Rate reverse reaction

  4. Conditions for Chemical Equilibria • A closed system • Constant temperature • Reversibility • Rates of opposing changes are equal

  5. Law of Chemical Equilibrium aA + bB ↔ cC +dD

  6. Le Châtelier’s Principle • You can use Le Châtelier’s Principle to predict how changes in concentration, volume (pressure), and temperature affect equilibrium

  7. Solubility Product Constant • The solubility product constant represents the concentrations of the products of a dissociation reaction (a in reaction in which a solid dissociates into aqueous ions). • The solubility product is found by multiplying the concentration of the solid by the equilibrium constant.

  8. Equilibrium is reached in a dissociation reaction when the rate of the dissociation is the same as the rate of recrystalization.

  9. Last topic in Chemistry 40s!! Starting now...

  10. Ion Product of Acids and Bases • Pure water undergoes a small degree of ionization • Only two molecules out of one billion will ionize 2H2O(l) ↔ H3O+ (aq) + OH-(aq) • Recall the definition of an acid and a base.

  11. Dissociation Constant of Water (Kw) • In pure water, the [H3O+] and [OH-] at 25oC are experimentally measured as 1x10-7 mol/L • K w = [H3O+][OH-] • K w = (1x 10-7)(1 x 10-7) • K w = (1 x 10-14)

  12. Every water solution is neutral, acidic, or basic • A neutral solution occurs when the hydronium ion concentration is equal to the hydroxide ion concentration • An acidic solution occurs when the hydronium ion concentration is greater than the hydroxide ion concentration • A basic solution occurs when the hydronium ion concentration is less than the hydroxide ion concentration

  13. pH • Most concentrations of hydronium ions are very small (around 4x10-8 mol/L), so a scientist named Soren P. Sorenson proposed the idea of the potency of hydrogen • Or simply the pH scale of a solution

  14. Calculating pH • pH is calculated as follows: • pH= log[H3O+] • Similarly, we can calculate a potency of hydroxide (pOH): • pOH= log[OH-] • Together: pH + pOH = 14

  15. Strengths of Acids and Bases Recall: • Strong Acid • Completely dissociates into ions • Strong Base • Completely dissociates into ion

  16. Weak Acids • Dissociate only slightly into ions HA(aq) + H2O(l) ↔ H3O+ (aq) + A-(aq) • Ka is called the acid dissociation constant

  17. Weak Bases • Dissociate only slightly into ions • HB(aq) + H2O(l) ↔ BH2+(aq) + OH-(aq) • Kb is called the base dissociation constant

  18. Questions?

  19. Review for tomorrow • Pg. 458 • Questions: 3, 10-18

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