Chem 1A03 Exam

Standard enthalpy of formation (standard heat of formation), H°f

change of enthalpy that occurs in the formation of 1 mole of substance from its constituent elements, with all substances in their standard states

standard state of C

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manipulating thermochem eqns (delta H values)

Standard enthalpy of formation of a pure element in its reference form is 0

- Reversing a rx = reverse sign of delta H

- Summing rx = sum delta H values

- Multiplying rx by a factor = multiply delta H by same factor

Include enthalpies of any phase change

- Moles AND phase must cancel out

- Ex: if want to cancel out 2H2O (l), on both sides must be both (l) not g or s or aq

- If one was (l) and another (g) then you would need a phase change and energy needed for it

spontaneous rxs have pos or neg delta G

neg

units for entropy

J/mol K

Heat capacity

(C): amount of heat needed to change the temp of a system by 1 degree in celsius or kelvin

Bomb calorimeter

- system isolated from surroundings

- Constant volume experiment; can't exchange matter or energy

- Work will be 0, change of volume is 0 (bc volume is constant)

- Qcalorium includes the water bath, stirring rod (everything else that is not the rx)

from gas to solid = heat released or needed?

heat is released

going from solid to gas = heat released or needed?

heat is needed

standard state of O2

O2 (gas)

standard state of Br2

Br2 (l)

standard state of Li

Li (s)

any element in standard state will have heat of formation of ___

zero

extensive vs intensive property

extensive: depends on how much substance you have; Ex: mass

Intensive property: does not depend on how muchs substance you have; Ex: density

what will delta G be when there is a phase change and at eqb

zero

when is entropy zero

pure, perfect crystal at 0K

bonds forming what is H value

H is neg (energy released)

bonds breaking what is H value

H is pos (energy needed)

spontaneous processes result in an increase or decrease in entropy of the universe?

increase

- S must be pos for a spontaneous rx

Spontaneous rx

anything that happens on its own

- Dependent on temp

- Ex: water freezing in -6 weather is spontaneous but water freezing in 10 degrees is not

Allotropes

diff ways for atoms to organize themselves

- Carbon can be diamond and carbon (but graphite is favoured)

- Allotropes are different forms of the same element and have different standard molar enthalpies

- P4 is the standard state of phosphorus but not thermodynamically favoured

why is energy released when ATP combines with water to produce ADP

- breaks a weak P-O bond

- forms a stronger P-O bond

- breaks the O-H bond of water

- form a weaker O-H bond

- more energy released when forming P-O bond than the energy needed to break the O-H bond

- Gibbs energy released in the ATP hydrolysis is enough

to make ATP

non-spontaneous; requires energy

- vs breaking ATP and forming ADP

conditions that increase entropy

- increase volume

- increase # of atoms per molecule

- increase # of independent moving particles

- increase temp

- spontaneous process

conditions that decrease entropy

- decreasing temp

- decrease # of atoms in molecule

- decrease # of independent moving particles

- decrease temp

- non spontaneous process

- system at eqb

- reversible process

oxidation

LEO

- losing e-

reduction

GER

- gaining e-

OA

causing reduction

RA

causing oxidation

which metals usually undergo redox change

transition metals

movement of e- in electrochem cells

e- moves from anode to cathode generating voltage

what does the salt bridge do

movement of cations and anions through salt bridge maintains electroneutrality in soln

anode

oxidation (think vowels)

- e- produced at anode and does to cathodes

- anions go to anode

M --> M+ + e-

cathode

reduction (think consonants)

- e- being consumed so gains mass

- cations go to cathodes

M+ + e- --> M

galvanic (voltaic) cell

results from spontaneous chem rxs

electrolytic cell

uses electricity to accomplish non-spon chemical change

cell diagram

- LEFT: oxidation half cell; anode

- single line = phase change

- double line = salt bridge

- RIGHT: reduction; cathode

- far left and right will be the cathode and anode (the solids)

standard electrode/redox potentials, degree E

tendency for a redox rx to occur

- more pos E values = rxs w strong tendency to go to right hand side (reduction); most easily reduced

- more neg values indicate rxs with strong tendency to proceed to left hand side (oxidation); most easily oxidized

when E degree cell > 0

rx is spontaneous

- intensive property (doesn't depend on the amount of substance reacting)

magnitude of cell potential (E degree cell) indicates

driving force for cll

- E degree cell of 1.1 more likely to go to completion than E degree cell of 0.46

how to tell if a rx is spontaneous based on Ecell and G value

Ecell > 0 and G < 0

if anode and cathode are the same, then E degree cell is

zero

e- chooses the path of

least resistance

- e- will choose to reduce water than potassium

Li-ION batteries

63% of portable batteries worldwide since being commercialized by Sony in 1990

- SONY used patents of a Canadian company (Moli-Energy)

- In 2016, global lithium-ion battery production was 28 gigawatt-hours with 16.4 GWh in China (could power bill of cell phones)

why are Li batteries superior to other electrochem energy storage devices

is a battery that is lightweight and has small volume

- prob: expensive and can start a fire (dangerous)

- if x is 0 then no Li in cathode rx

If M is able to displace Ag+ but not Cu2+ what is the standard reduction protential

Cu2+ < E°cell < Standard red potential Ag+

Higher reduction potential =

more easily reduced

Rxs for which E depends on pH

have either H+ or OH- in the balanced eqn

- Rxs involved oxyacids and oxyanions whose central atom changes oxidation state

H+ will be on the left side of a rx when...

There is a reduction of an oxoanion bc there is a decrease of oxidation states and loss of oxygen atoms

- Ex: CIO3 → CIO2

- SO42- → SO2

OH- will be on the right side of the rx when...

In a basic soln when you need to balance out the H

electrons flow from higher to lower conc or vice versa?

flow from lower to higher conc

entropy and enthalpy are state or path fcts?

state