unit 9: applications of thermodynamics

entropy (ΔS)

the measure of how dispersed/spread out the matter and energy of a system is (more spread out → higher entropy)

• +ΔS: higher entropy

• -ΔS: lower entropy

standard change in entropy

measure of how entropy changes during a process at some standard conditions

absolute entropy

entropy change as a substances ins heated from 0 Kelvin

gibbs free energy

measure of the thermodynamic favorability of a reaction at certain conditions

• ΔG < 0: thermodynamically favored

• ΔG > 0: not thermodynamically favored

• ΔG = 0: equilibrium

ΔG

change in free energy when forming 1 mole of substance from its elemental components at standard conditions

kinetic control

reactions when ΔG < 0 but do not happen at any significant rate at a given temperature

coupling

a thermodynamically favorable reaction occurs alongside an unfavorable one, using intermediates to get the desired product

electrochemical cell

chemical energy is converted to electrical energy using redox reactions

galvanic cell

generate electricity by using redox equations that are thermodynamically favorable

electrolytic cell

use a power supply to drive a thermodynamically unfavorable reaction

electrochemical potential

measured in volts

half-reactions

reaction of oxidation or reduction component alone

• not dependent on the number of electrons or coefficients in balanced half reaction equations

Q < 1

more reactants, stronger forward reaction, increased voltage, new Ecell is > standard Ecell

Q > 1

more products, stronger backward reaction, increased voltage, new Ecell is < standard Ecell