7.06 Equilibrium Lab Report

Question: what is the drive/goal of most reactions?
Answer: to find chemical stability, or equilibrium
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Question: equilibrium
Answer: a state where opposing forces/influences are balanced
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Question: dynamic reaction
Answer: reaction that goes in both directions
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Question: dynamic equilibrium
Answer: a state of balance where the rates of the forward and reverse reactions are equal

- even though the forward and reverse reactions continue to occur

A + B β‡Œ C + D
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Question: in a "closed system," reactions reach dynamic equilibrium when:
Answer: 1) rate of forward reaction = rate of reverse reaction
2) concentrations of reactants & products stay constant
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Question: many reactions stop just before completion because:
Answer: a reverse reaction begins

(products in reaction react to reform original reactants (in reversible reactions))
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Question: true or false: all chemical reactions are reversible
Answer: true, theoretically

(although some occur much easier than others)
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Question: example of reaching dynamic equilibrium:
Answer: as concentration of reactant (2NOβ‚‚) ↓ during a reaction, rate of reaction also ↓

at the same time, concentration of product (Nβ‚‚Oβ‚„) ↑, which tips reaction in opposite direction. this means rate of reverse reaction (Nβ‚‚Oβ‚„ β†’ 2NOβ‚‚) ↑ as rate of forward reaction ↓

eventually, rates of forward and backward will be equal
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Question: chemical equilibrium does NOT mean there are equal ______ of reactants and products

it DOES mean their concentrations don't ______, as long as there's no change in conditions such as temp. or pressure
Answer: concentrations

change
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Question: examples of physical changes in which dynamic equilibrium can occur
Answer: - evaporation/condensation
- dissolving/cyrstallization

ex: salt dissolves in water (forward) β†’ reaches saturation
point β†’ begins to crystallize again (reverse)
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Question: law of mass action
Answer: a general description of equilibrium, including an equation that defines the equilibrium constant

- 1864, Norweigan chemists Cato Guldberg and Peter
Waage
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Question: equilibrium constant (K)
Answer: - the value obtained when equilibrium concentrations are plugged into the 'law of mass action' equilibrium expression:

[C]ΚΈ x [ D]αΆ»
K = -------------- (K = [products]/[reactants])
[A]Κ· x [ B]Λ£

(brackets = concentration, in molarity (M), of solutions and gases; pure liquids/solids = exempt, and their addition/removal usually doesn't affect the value of K)

- in the forward reaction, 'w' moles of 'A' interact with 'x' moles of 'B' to produce 'y' moles of 'C' and 'z' moles of 'D': wA + xB β‡Œ yC + zD


- constant for a given system at a given temperature
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Question: equilibrium position
Answer: given set of equilibrium concentration values

- depends on initial concentration of each substance
- can be predicted based on the value of the equilib. constant ( 1 = [1]/[1]; 10 = [10]/[1]; .10 = [1]/[10])
- if k < 1, forward reaction won't get very far before
dynamic equilibrium is reached

- discussed more in 7.07; position shifts depending on different factors such as concentration, pressure and temperature
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Question: true or false: introduction of a catalyst will NOT affect the equilibrium position
Answer: true
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Question: graphs
Answer: check last 2 pages of 7.06 notes for graphs

('rate of reactions' graph - compares reaction rate over time; shows what is equal when system is at equilibrium)

('concentration' graph - shows changes in concentration of reactants + products over time;
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