Hon Chem-Electrochemistry

OIL RIG

oxidation is losing e-(- to +), reduction is gaining e-(+ to -)

Oxidation half rnx

the e- is written as a product

Reduction half rxn

e- is written as a reactant

Determining Oxidation numbers: Rule of free elements

They will be ZERO, Ni, Cu, O2 are all netural on their own

Determining Oxidation numbers: Rule of monoatomic ions

they are equal to the ion charge. Li+,Cu 2+, Br- are equal to the ion charge

Determining Oxidation numbers: Rule of sum of oxidation numbers

They must add to the overall charge.

Netural compounds - sum of oxidation numbers=0

Polyatomic ions - sum of oxidation numbers= poly ion charge

Determining Oxidation numbers: Always in a compound or polyatomic ion… Oxidation number of F is always

-1

Determining Oxidation numbers: Always in a compound or polyatomic ion…Oxidation number of H is

+1(excluding metal hydride)

Determining Oxidation numbers: Always in a compound or polyatomic ion…Oxidation number of O is

-2(except in peroxides)

Electrochemical cells

voltaic cells, galvantic cells. The E0 is ALWAYS positive, because this means that they occur spontanously(naturally)

What if E0 is negative?

This is electrolysis, where it won’t happen on it’s own, but is still able to occur

Equation to find E0

E0(Reduction)-E0(Oxidation)

E is always in

VOLTS

Red cat standing on an Ox

Reduction occurs at the cathode, and Oxidation occurs at the anode

When writing the balanced rxn or half rxn of whats being ox/red… Always remember to

BALANCE EQUATIONS AND CONSIDER THE LAW OF CONVERSATION OF MASS, some half rxns will have to be multipled depending on the # of e-, and look out for any diatomic elements that will effect the balance too(H2 for example)

Electrochemical cell device

a device that generates electrical energy from chemical reactions or uses electrical energy to drive chemical reactions.

The e- flow will always happen from the ___ to the ____

ANODE TO CATHODE

Will the anode gain/lose mass?

Lose mass

Will the cathode gain/lose mass?

Gain mass

What does the salt bridge do?

Prevents + and - ion buildup

Where do cations flow to in the salt bride?

To the cathode

Where do anions flow to in the salt bridge?

To the anode

Cell notation rule

Anode ox Rxn|Anode ox product||Cathode red reactant|Cathode red product

ALWAYS for spontaneous cells…

Electron flow from anode to cathode, entire “circuit” must be present, and E0 must be +

Electrolysis

Putting in energy to force the nonspontaneous change(if non-spon process has an E0 of -0.40 volts, it needs 0.40 volts)

Molten ionic compounds

The ions present are the ones only in the compound, this is more expensive and risky to make

Aqueous ionic compounds

The ions of a compound plus water are all present

What is special about water in an Aqueous ionic compound?

It shows up twice on the table, so it can be reduced and/or oxidized

In an aq solution of an ionic compound, the half rxn with the more positive reduction potential will be…

Reduced

In an aq solution of an ionic compound, the half rxn with the more negative reduction potential will be…

Oxidized

Electrical current unit

Amps(A)

Electrical charge units

Coulombs C

1 mole of electrons=

96500 coulombs=1 faraday

Whats important to doing electrolysis math first?

WRITE APPLICABLE HALF RXNS FIRST

What is an important detail to writing half rxns for electrolysis math?

If given a compound, but you only need to find an answer for one element or use one element of the compound, the other one can be omitted. Pay special attention to the wording and what it is asking for!