equilibrium. chemical equilibrium review most chemical reactions do not go to completion. they...
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Equilibrium
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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
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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
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Conditions for Chemical Equilibria
• A closed system• Constant temperature• Reversibility• Rates of opposing changes are equal
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Law of Chemical Equilibrium
aA + bB ↔ cC +dD
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Le Châtelier’s Principle
• You can use Le Châtelier’s Principle to predict how changes in concentration, volume (pressure), and temperature affect equilibrium
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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.
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• Equilibrium is reached in a dissociation reaction when the rate of the dissociation is the same as the rate of recrystalization.
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Last topic in Chemistry 40s!!
Starting now...
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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.
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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)
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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
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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
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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
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Strengths of Acids and Bases
Recall:• Strong Acid
– Completely dissociates into ions• Strong Base
– Completely dissociates into ion
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Weak Acids
• Dissociate only slightly into ions
HA(aq) + H2O(l) ↔ H3O+ (aq) + A- (aq)
• Ka is called the acid dissociation constant
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Weak Bases
• Dissociate only slightly into ions• HB(aq) + H2O(l) ↔ BH2
+ (aq) + OH- (aq)
• Kb is called the base dissociation constant
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Questions?
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Review for tomorrow
• Pg. 458– Questions: 3, 10-18