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What two conditions need to be met for a reaction to be spontaneous?
ΛG<0 and K>1
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What is the Gibbs Free Energy equation?
ΛG= ΛH- TΛS
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What is entropy?
- A change in randomness
- Increases with all spontaneous reactions (2nd law of thermodynamics)
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What is the first law of thermodynamics?
Energy cannot be created or destroyed
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What is thermodynamics?
A prediction about whether or not a reaction will occur under the given conditions
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How to calculate ΛG in standard conditions:
ΛGrxn= ΛHrxn- TΛSrxn
Or
ΛGrxn= ΣnΛGf (products) - ΣnΛGf (reactants)
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How to calculate ΛG under non-standard conditions:
ΛG= ΛG(naught)+ RTlnQ
Where R = 8.314 J/mol*K
- When at equilibrium:
- ΛG= -RTlnK
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What are the factors that affect entropy?
- State: gas>liquid>solid
- Molecular mass and complexity: more = more entropy
- Allotropy: More irregular = higher
- Dissolution: Solution>pure solvent/ solute alone
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What are the standard states?
- Gas: pure gas at 1 atm
- Solid Liquid: Pure solid/liquid in it's most stable form
- Temperature: 25C
- Solution: Solute concentration 1M
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What is the faraday constant?
96,485 F
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What is solubility?
How well something dissolves from a solid to an aqueous substance
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Is E(cell) positive or negative when a reaction is spontaneous?
Positive
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Nernst Equation
Ecell= E(cell)- 0.0592/n(logQ)
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Calculating E(cell)
E(cell)= E (reduction)- E(oxidation)
(Cathode-anode)
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What is controlled by entropy and enthalpy?
Spontineity (ΛS)
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Calculating standard entropy change (spontaneity)
ΛSrxn= ΣnΛS (products) - ΣnΛS(reactants)
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Calculating change in enthalpy (ΛH)
ΛHrxn= ΣnΛH (products) - ΣnΛH (reactants)
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Factors that affect solubility
- Common ion effect- Adding ions shifts equation to the left, because [] of ions has increased
- pH effect- Metal hydroxides are more soluble when the pH is low (basic)
- Compounds containing anions that are the conjugate bases of weak acids are more soluble with a low pH (basic)
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How is precipitation predicted with Q values?
- Q>1, precipitation forms. Reaction shifts left
- Q<1, no precipitation forms. Reaction shifts right
- Q=1, precipitation on the cusp of forming. Reaction does not shift
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What is Ksp
The solubility constant
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How does ΛS effect entropy?
- ΛS>0, more random. Favors spontaneity
- ΛS<0, less random. Does not favor spontaneity
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On the standard electrode potential chart, the most negative is the best ____ agent
Reducing
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On the standard electrode potential chart, the most positive is the best ____ agent
Oxidizing
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What occurs at the anode and what is its charge?
- Oxidation
- Negative (anion)
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What occurs at the cathode and what is its charge?
- Reduction
- Positive (cation)
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What is the common oxidation number of O2?
-2
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What is the oxidation number of an element?
0
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What is the oxidation number of a monatomic ion?
It's charge
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