Chemistry 12 - Unit 5: Electrochemistry

electrochemistry deals with the…

relationship between electricity and chemical reactions

electrochemical reactions are called…

reduction-oxidation reactions

short form of reduction-oxidation reactions

redox

all redox reaction involve the…

transfer of electrons from one substance to another

the activity of an element is…

a measure of its ability to replace another element in a compound

the skeletal reaction shows only…

the reactants and products that are part of the reaction; no spectators

the skeletal reaction does not need to be…

balanced

spectator ions

ions that do not participate chemically

skeletal reactions can be simplified into…

two half-reactions

electrochemical cell

two separate half cell compartments joined by a salt bridge

oxidation reaction

a half-reaction in which a species loses electrons

reduction reaction

a half-reaction in which a species gains electrons

OIL

oxidation is losing

RIG

reduction is gaining

what half-reaction occurs first?

oxidation

oxidizing agent

chemical species that causes the other reagent to be oxidized; becomes reduced

reducing agent

chemical species that causes the other reagent to be reduced; becomes oxidized

half-reactions always include…

e’s

redox reactions never show…

e’s

for a reduction half-reaction, electrons are always found on the…

reactant side

for an oxidation half-reaction, electrons are always found on the…

product side

oxidation number definition

the charge that an atom would possess if the chemical species containing the atom were composed of ions

electronegative elements attract____ so that they tend to have______

electron density; negative oxidation numbers

oxidation number of atoms of elements

0

oxidation number of simple monatomic ions

the ion charge

oxidation number of alkali metals

1

oxidation number of alkaline earth metals

2

oxidation number of fluorine

-1

oxidation number of hydrogen in most molecules or ions

1

oxidation number of hydrogen in metal hydrides

-1

metal hydride is when…

hydrogen is bonded to elements less electronegative than itself

oxidation number of oxygen in most molecules or polyatomic ions

-2

oxidation number of oxygen in peroxides

-1

oxidation numbers add up to the…

overall charge of the molecule or ion

ionic compound can be simplified into…

ions

all atoms of the same element in a molecule must have…

equal oxidation numbers

during an oxidation, the number of attached oxygen atoms…

increases

during an reduction, the number of attached oxygen atoms…

decreases

what can be predicted using a table of Standard Reduction Potentials

the spontaneity of a redox reaction

what are generally stronger oxidizing agents?

nonmetals

why are nonmetals stronger oxidizing agents?

greater electronegativity

what are generally stronger reducing agents?

metals

why are metals stronger reducing agents?

lower electronegativity

why are individual half reactions written using equilibrium arrows?

to show that the reaction could proceed in either direction

what arrow is used if the reaction is one half of a specific redox reaction?

one way

a reaction always proceeds away from the…

stronger oxidizing agent

when two half-cells are joined, the higher half-reaction will undergo…

reduction

when two half-cells are joined, the lower half-reaction will undergo…

oxidation

a reaction will only be spontaneous if and only if there is a…

reactant to be reduced on the left side which is above a reactant to be oxidized on the right side

a redox reaction must be balanced by its…

atoms and charges

memory aid to remember how to balance half reactions

major OH-

to convert a half reaction to basic conditions, you must…

use the water equilibrium equation to cancel all the H+ ions

the oxidation number ____ during a reduction reaction

decreases

the oxidation number _______ during a oxidation reaction

increases

disproportionation reaction

a redox reaction in which the same species is both reduced and oxidized

a redox titration requires both an…

oxidizing agent and a reducing agent

in a redox titration, the indicator is a…

reactant

a colour change occurs when…

the reactant has been consumed

common oxidizing agent

potassium permanganate

MnO 4- (potassium permanganate) colour

purple

Mn2+ colour

colourless

other common oxidizing agents

dichromate and chromate

Cr2O7 2- (dichromate) colour

orange

CrO4 2- (chromate) colour

yellow

Cr 3+ colour

colourless

common reducing agents

NaI and KI

titration involving the iodide ions typically involve…

two steps

at the equivalence point of a titration using iodide, the solution is no longer what colour?

blue

each half cell consists of an…

electrically conducting electrode in contact with a salt solution

the oxidizing agent tends to gain electrons by…

pulling them away from the reducing agent

where does oxidation or reduction occur?

at the surface of each electrode

anode

electrode where oxidation occurs

cathode

electrode where reduction occurs

electrons in an electrochemical cell travel from the…

anode to the cathode

in an electrochemical cell, mass of the anode…

decreases

in an electrochemical cell, mass of the cathode

increases

an electrochemical cell can not operate without a salt bridge because the…

half cell compartments would become polarized

job of the salt bridge is to…

maintain electrical neutrality in each solution throughout the cell’s operation

cations go to the

cathode

anions go to the

anode

voltage/electrical potential definition

the work done per electron transferred

E^o

standard reduction potential

for an oxidation reaction, the sign of the half-cell voltage is

reversed

the standard cell potential of a cell is the…

sum of the voltages of each half cell reaction

a redox reaction is spontaneous if the cell potential is…

positive

if the potential of a cell is negative, the reaction is expected to be…

spontaneous is the reverse direction

the surface area of an electrode has…

no effect on the cell potential

temperature of 25C, solution concentration of 1M, elements in their standard state, and gas pressures of 101.3 kPa (1 atm)

standard condtions

as a cell operates, the reactant ion concentration_____ and the product ion concentration _____

decreases, increases

as ion concentration changes in a cell….

the voltage of the cell will decrease until it becomes 0V

dead cells refer to a…

static equilibrium of forces; both reactant and product ions are pulling on the electrons equally in opposite directions