AP Chemistry: Unit 9

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53 Terms

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Entropy

the dispersal of matter of energy → changes in entropy measure how dispersed the matter or energy is in a system.

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Increased disorder, increased dispersion, and increased temperature will yield

a higher entropy value

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Entropy of a gas increases as

the number of gaseous particles increases and the volume increases

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Unit of entropy

J/mol*K

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Unit for enthalpy

kJ/mol

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ΔS°=

Σ(S° of the products)-Σ(S°reactants)

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Gibbs Free Energy Change

describes whether a reaction is thermodynamically favorable or unfavorable depending on enthalpy and entropy

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ΔG°=

Σ(ΔG° of the products)-Σ(ΔG°reactants)

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Unit for ΔG°

kJ/mol

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Positive entropy value

Favorable

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Negative entropy value

Unfavorable

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Positive free energy value

Unfavorable

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Negative free energy value

Favorable

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ΔG°=

ΔH°-T(ΔS°)

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If entropy (+) and enthalpy (-)

ΔG° is favorable at all temperatures

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If entropy (-) and enthalpy (+)

ΔG° is favorable at no temperatures

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If entropy (+) and enthalpy (+)

ΔG° is favorable at high temperatures - Driven by entropy

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If entropy (-) and enthalpy (-)

ΔG° is favorable at low temperatures - Driven by enthalpy

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Kinetic control

describe specific kinetic controls, such as high activation energy, and its effect on the rate of a thermodynamically favorable reaction. (Slow rate of a thermodynamically favorable reaction)

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What effect does thermodynamic favorability have on the equilibrium constant?

It will yield a higher equilibrium constant since the products are favored

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If ΔG°=0

System is at equilibrium

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If ΔG°>0

K<1

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If ΔG°<0

K>1

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k=

e^ΔG/RT

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ΔG°=

-RTI

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How can we make a thermodynamically unfavorable process occur?

Through a coupled reaction (combining it with another favorable reaction with a common intermediate)

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How do we find the ΔG° of a coupled reaction mechanism?

Using Hess’s Law principles to make sure the overall ΔG° for the reaction will be favorable.

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Galvanic cells (Voltaic)

they will convert the energy released by a thermodynamically favorable redox reaction to electrical energy

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Electrolytic Cells

they will use electrical energy to drive a thermodynamically unfavorable redox reaction

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Anode

where the oxidation reaction takes place

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Cathode

where the reduction reaction takes place

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Salt bridge

allows for the movement of ions between the half cells in galvanic cells. It contains an inert ionic solution.

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Cations from the salt bridge flow into the

cathode

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Anions from the salt bridge flow into the

anode

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The anode will experience what change in mass?

Lower mass (s)→(aq)

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The cathode will experience which change in mass?

Higher mass (aq)→(s)

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Galvanic cells will have what type of voltage?

Positive voltage

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Electrolytic cells will have which type of voltage?

Negative voltage

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Electrolytic cells require what?

A power source and an aqueous solution/molten solution of salt

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Reduction potential (E=volts)

describes the electrical potential changes between the oxidation and reduction processes occurring in the half-cells

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To find the oxidation potential we…

change the sign of the voltage found in the reduction potential value.

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In tables that show reduction potentials, the higher row ones will be

the most favorable.

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E°cell=

E°cathode-E°anode

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Coefficients are negligible when we are

FINDING THE REDUCTION AND OXIDATION POTENTIALS TO FIND THE E°cell

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Thermodynamically favorable cells will have a ___ E°cell

Positive (Galvanic)

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Thermodynamically unfavorable cells will have a ___ E°cell

Negative (Electrolytic)

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ΔG°=

-(moles)(faraday’s constant)(E°cell)

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As we approach the formation of more products, the cell potential

decreases

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Charge flow in electrolysis

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Current

Amperes - Coulombs/Seconds

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Time

Seconds

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Faraday’s Constant

Coulombs/mole e-

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mol e-

refers to the ratio between the reactant/product with the number of e- involved in oxidation or reduction