AP Chem - Unit 9

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39 Terms

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entropy (S)
**the measure of disorder** in the dispersal of matter or energy in a sample of matter
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changes in entropy (𝚫S) measure
how dispersed the matter or energy is in a particular system
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entropy increases when
matter becomes more dispersed

in cases where:

* phase changes from solid to liquid and from liquid to gas
* individual particles become more free to move and occupy a large volume
* volume of a gas increases
* gas molecules are able to move within a larger space at the same speed
* number of moles of product > reactants
* temperature increases
* distribution of KE among gas particles broadens as temperature increases
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entropy change
𝚫S reaction = ΣS products - ΣS reactants
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entropy is measured in
joules
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at absolute entropy
every substance has a nonzero value
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when calculating entropy the
number of moles of each substance (in the balanced equation) must be considered
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signs of entropy change can be predicted
by the state and number of moles of reactants and products
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\+𝚫S
* solid → liquid → gas
* number of moles increase from reactant to products
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\-𝚫S
* gas → liquid → solid
* number of moles decreases from reactant to products
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gibbs free energy (G)
describes whether a reaction is thermodynamically favorable or unfavorable
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changes that are thermodynamically favorable
* proceed to equilibrium without external intervention
* does not happen quickly just because it is favorable
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gibbs free energy change (𝚫G)
𝚫G reaction = ΣG products - ΣG reactants
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𝚫G < 0
thermodynamically favorable
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𝚫G > 0
thermodynamically unfavorable
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with 𝚫G = ΔH - TΔS
thermodynamically favored can be predicted from the signs of ΔH and ΔS
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MEMORIZE FOR UNIT 9
knowt flashcard image
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processes under kinetic control
* thermodynamically favorable
* large activation energy and thus very slow
* catalysts have no effect on thermodynamic favorability
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products are favored at equilibrium
* thermodynamically favored
* ΔG° < 0 and K > 1
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reactants are favored at equilibrium
* thermodynamically unfavored
* ΔG° > 0 and K < 1
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free energy and equilibrium constant relationship
knowt flashcard image
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coupled reaction
* an unfavorable reaction can be coupled with a favorable one to make the process occur
* can be coupled if the two reactions share a common intermediate
* hess’s law is applied to determine the ΔG
* the sum must be negative making the reaction favorable
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electrochemical cell
a device that can convert energy released by a favorable reaction to electrical energy or can drive a unfavorable reaction

* contains and anode and cathode
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cathode
* where oxidation occurs
* cations
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anode
* where reduction occurs
* anions
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galvanic (voltaic) cells
* thermodynamically favorable reaction
* anode and cathode in separate half cells
* salt bridge needed - allows for movement between half cells
* necessary for current to flow in the circuit
* produces electrical energy
* + voltage value
* electrons flow from anode to cathode
* thermodynamically favorable reaction 
* anode and cathode in separate half cells 
* salt bridge needed - allows for movement between half cells 
  * necessary for current to flow in the circuit 
* produces electrical energy 
* + voltage value 
* electrons flow from anode to cathode
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electrolytic cells
* thermodynamically unfavorable reaction
* anode and cathode in the same chamber
* power source needed (no salt bridge)
* uses electrical energy
* - voltage values
* electrons flow
* anode → power source → cathode
* occurs in ionic solution or liquid
* cations → cathode and anions → anode
* thermodynamically unfavorable reaction
* anode and cathode in the same chamber
* power source needed (no salt bridge) 
* uses electrical energy 
* - voltage values 
* electrons flow
  * anode → power source → cathode 
* occurs in ionic solution or liquid 
* cations → cathode and anions → anode
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electric potential difference (voltage) involves
* a reaction occurring in an electrochemical cell
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E°red
* standard reduction potentials
* 1 M solutions, 1 atm of pressure for gases, 25℃
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to get oxidation potentials
* the reduction half-reaction and sign of voltage must be reversed
* do not multiply stoichiometric coefficients in the equation
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more positive the E°V
more favorable the reduction
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cell’s standard potential (E°cell)
* calculated with E°cell = E°cathode - E°anode
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voltaic cells (favorable reactions)
positive overall cell potential
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electrolytic cells (unfavorable reactions)
negative overall cell potential
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ΔG° is proportional to
* - cell potential for the reaction when its constructed
* moles of e- transferred
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ΔG° = -nFE°cell
* +E°cell = -ΔG°
* -E°cell = +ΔG°

\
F = faraday’s constant = 96485 C/m e-