Exam 3: ch 19 + 20 Flashcards by Ella Fischer

enthalpy

heat absorbed or released by a system during a constant pressure process

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entropy

measure of randomness/disorder in a system

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1st law of thermodynamics

-energy can not be created or destroyed, but only converted or transferred
-delta E (sys)=q+w

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spontaneous process

proceeds w/o any outside assistance

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reverse of spontaneous

nonspontaneous

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nonspontaneous

proceeds w/ outside assistance only

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factors that affect spontaneity

temperature and pressure

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reversible process

system changes so that the system and surroundings can return to original state

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irreversible process

cannot be undone by exactly reversing the change

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are spontaneous process reversible

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is entropy a state function

yes

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state function

actual path is not relevant to final answer

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delta S (when given heat and temp.)

=q/T

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2nd law of thermodynamics

the entropy of the universe increases in any spontaneous process

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delta S (univ) >0

irreversible process, spontaneous

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delta S (univ)= 0

reversible process

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microstate

a single possible arrangement of position and kinetic energy of molecules

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boltzman equation

S=kln(w)

w- # of microstates
k- boltzman constant (1.38 x 10^-23)

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more microstates =

more entropy

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degrees of freedom (DOF)

types of motion

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translation

movement of entire molecule

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vibration

movement of atoms w/in molecule
(stretching/ contracting of bonds/angles)

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rotational

movement about an axis

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the # of microstates possible increases w/

increase of: volumes, temperature, and number of atoms

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entropy order of states of matter

gas>liquid>solid

when the # of gas molecules increases

the entropy of a system increases

delta n > 0

increase in entropy

delta n < 0

decrease in entropy

entropy of a pure crystalline substance at absolute zero is...

zero

enthalpy, entropy, and free energy formation of a rxn

products- reactants, use given values multiplied by coefficients

standard entropy for elements

zero

entropy unit

J/mol x K

enthalpy and fee energy unit

kJ/mol

delta G =

delta H (sys) - (T)(delta S (sys))

delta G is negative ...

spontaneous

delta G = 0 ...

system at equilibrium

delta G is positive ...

nonspontaneous

delta G (under any conditions) =

delta G (naught) + RTln(Q) Q-rxn quotient R- 8.314

delta G (naught)=

-RTln(k)

+ delta H and - delta S

+ delta G, nonspont. at all temps

- delta H and +delta S

- delta G, spont, at all temps

both delta H and S are neg.

spont. at low temps

both delta H and S are pos.

spont. at high temps

electrochemistry

study of relationships between electricity and chemical reactions

oxidation numbers

used to track which element looses or gains e- during a rxn

oxidation

loss of electrons, ox # increases

reduction

gain of electrons, ox # decreases

oxidizing agent

species which got reduced

reducing agent

species that got oxidized

for "in acidic soln"

do normal balancing procedure

for "in basic soln"

do normal acidic soln procedure, then use OH- to balance out rxn

voltaic (galvonic) cells

electrochemical cells w/ 2 half rxns separated into containers

spont. redox rxn electron transfer

anode to cathode, energy is released

anode

oxidation half rxn

cathode

reduction half rxn

salt bridge/ porous cup does what?

keeps the charges balanced

do anodes loose or gain mass

loose

do cathodes loose or gain mass

gain

when loosing mass the concentration...

increases (vice versa)

electrons from from --- to ---- potential energy

high to low

electromotive force

potential difference between the anode and the cathode

cell potential (Ecell)

-measured in volts (V) - 1V = 1J/C

higher reduction potential=

more likely to be reduced

Ecell (naught)=

Ered (cathode)(naught) - Ered (anode)(naught)

strongest oxidizing agents have most ------ reduction potential

positive

strongest reducing agents have most----- reduction potential

negative

more positive E=

the cathode

delta G (naught)= -n ...

FE(naught)

faraday's constant, F =

96485 J/V mol

spont rxn has a ------ Ecell

positive

concentration cell

galvonic cell prepared w/ same material for anode and cathode

battery

portable, self contained electrochemical power source that consists of one or more voltaic cells, DC current

primary cells

can only discharge once (non-rechargeable)

secondary cells

rechargeable batteries, redox rxn can be reversed

lead-acid battery

-for combustion engines -reactants and products are solids -made w/ lead and sulfuric acid

Ni-Cd and Ni-metal hydride batteries

-lightweight, rechargeable -hydrides replace Cd

fuel cells

NOT BATTERIES, fuel is burned and converted to electricity (DC), source of energy must be continuously provided

hydrogen fuel cells are --------as efficient as combustion

twice

corrosion

the oxidation which leads to structural and mechanical failure

iron corrosion

rust

copper corrosion

patina

cathodic protection

introduce another metal which is easier to oxidize

Exam 3: ch 19 + 20 Flashcards

(82 cards)