Unit 9 - Thermodynamics and Electrochemistry

The entropy of an isolated system will always ____ (Second Law of Thermodynamics)

increase over time

when is enthalpy and entropy favored? (decreasing/increasing)

enthalpy favored when decreasing… (exothermic reactions favored)

entropy favored when increasing…

if both ΔH enthalpy (-) and ΔS entropy (+) are favored then what is true about temperature?

then the reaction will be favored (spontaneous) at all temps

if both ΔH enthalpy (+) and ΔS entropy (-) are UNFAVORABLE then what is true about temperature?

it will NEVER be favored (spontaneous) at any temp!!

If ΔH and ΔS are both +, the reaction is only (spontaneous) favored at..

high temps!

If ΔH and ΔS are both - the reaction is only (spontaneous) favored at …

low temps!

What is Gibbs Free Energy?

a measure of the thermodynamic favorability of a reaction

ΔG = ΔH - T(ΔS)

OR

ΔG = products - reactants

Ag₂CrO₄ has a ΔG=+68 kJ/mol is it soluble/insoluble?

insoluble because ΔG unfavorable (positive) so reaction to dissolve it wouldn’t be driven (atleast naturally..)

if its spontaneous in one direction it is ____ in the other

nonspontaneous

when combining two reactions what do you do with their ΔG? (add/multiple/subtract..)

add their ΔGs!

in galvanic cell anode ____ and cathode ___ in mass

anode decreases and cathode decreases in mass (cat gets fat..)

purpose of salt bridge

transfer of ions to keep charges all balanced

flow of ions in salt bridge (where do cations and anions go?)

anions towards anode

cations toward cathode

the ions in the salt bridge need to be ___

inert or nonreacting with the ions in the solutions

reduction takes place in the ___

cathode (red cat)

oxidation takes place in the ___

anode (an ox)

Galvanic cells are always…

thermodynamically favorable (spontaneous)

Which one is the anode and cathode from these reduction half reactions?

Fe²⁺ + 2e^- → Fe -0.44V

Cu²⁺ + 2e^{- → Cu} +0.34V

use E_cell = E_cathode - E_anode

and plug in either V value for either cathode or anode until you get a postive answer

Fe as cathode, Cu as anode : (-0.44V) - (0.34V) = -0.78 NOPE!

Cu as cathode, Fe as anode : (0.34V) - (-0.44V) = +0.78V YES!

If E°_cell has that little degree symbol it means…

it’s at standard conditions

What are standard conditions?

Temp= 25C

Concentration_(aq) = 1.00M

Pressure of all gases = 1.00 atm

In a galvanic cell, E_cell is thermodynamically favorable when it is positive/negative

positive E cell

Lets say E_cell is negative how would we drive the reaction forward?

with an electrolytic cell!! since -E_cell is unfavorable and wouldnt work in galvanic cell