G Chem Class 6 - Electrochemistry and Nuclear Chemistry

What is reduction?

Gain electrons (lose bonds to more EN atoms, gain bonds to less EN atoms)

What is oxidation?

Losing electrons (gain bonds to more EN atoms, lose bonds to less EN atoms)

What are rules of oxidation states?

1. Zero for any element in standard state

2. Sum of oxidation states is charge of molecule

3. Group 1 metals are +1 and group 2 metals are +2

4. Fluorine is -1

5. Hydrogen is +1 if bonded to more EN than carbon, -1 if bonded to less EN than carbon, zero if bonded to carbon

6. Oxygen is -2

7. Halogens have -1, atoms in oxygen family have -2

8. All of the same atom have same oxidation state in a molecule

What is a reduction potential?

How likely something is to be reduced

Flip the sign to get oxidation potential

What is a reducing agent?

Get oxidized

Cause others to gain electrons

Low reduction potentials

Ex: H2, neutral metals, MetalH (LiAlH4, NaBH4, etc.)

What are oxidizing agents?

Cause others to lose electrons

Become reduced

High reduction potentials

Ex: neutral non-metals, MetalO (MnO4-, CrO3, etc)

How to use cell potential it to calculate delta G?

Delta G inversely proportional to reduction potential

Delta G = -nF delta E

F = Faraday’s constant

How do you find cell potential?

Ecell = Ecathode - Eanode

What are cells?

Two or more electrodes made of conductive materials

Electrolyte bridge between them

Circuit connects them with resistor or power source

What is a galvanic cell?

No external power source

Spontaneous with a positive E cell

What is an electrolytic cell?

Non-spontaneous, negative Ecell

Part of complete circuit with external power source

How do galvanic cells work?

Electrons flow from anode to cathode

Electrolytes flow from cathode to anode

Pitting on the anode side (as metal there releases electrons and breaks down)

This discharges a battery (how batteries run out of charge)

In a galvanic cell, where do oxidation and reduction occur?

Anode: oxidation

Cathode: reduction

An Ox Red Cat

How do electrolytic cells work?

External power source

Electrons go from positive side of battery to negative side (but still anode to cathode of the cell)

Electrolytes move opposite to electrons (cathode to anode)

Pitting at the anode (oxidation)

Form more metal at the cathode (reduction)

This recharges a battery

What is a cathode?

Where reduction occurs, current flows towards, cations flow towards, plating occurs

Cations come to it with electrons

Positive in a galvanic cell, negative in electrolytic cell

H2 gas produced when water is reduced

What is an anode?

Oxidation, electrons flow away from it, anions flow towards it, plating occurs

O2 produced as water is oxidized

Negative in galvanic cell

Positive in electrolytic cell

What is electroplating?

Electrons can be used to do work

I =nF/t

Current = (moles of electrons)(faraday’s constant)/(time)

What is the Nernst Equation?

Ecell = E standard - RT/nF ln Q

At 25C: Ecell = E standard - 0.0592/n log Q

What is cerimetry?

Redox titration using Ce4+ + e- → Ce3+ as indicator

Equivalence point: average of Es

Half equivalence point: Emeasured = Ecell of species being titrated

2x equivalence point: Emeasured = Ecell of titrant

What is alpha decay?

2 protons and 2 neutrons (He nucleus) ejected from the nucleus of the species

Parent loses 2 from atomic number and 4 from mass number → identity of atom changes

Only happens with very large nuclei

Easily blocked, but very dangerous if it is not

What is beta emission?

One electron emitted

Atomic number increases by 1, mass number is the same → changes atom’s identity

Nuclei with high neutron to proton ratios

How do neutrons break?

Into a proton (mass 1, charge +1) and an electron (mass 0, charge -1)

Thus a neutron is mass 1, charge 0

What is positron emission?

Beta decay subtype

Positive electron emitted (mass stays the same, atomic number decreases by 1)

In nuclei with high proton to neutron ratio

What is electron capture?

Type of beta decay

Electron absorbed by nucleus (same atomic mass, atomic number decreases by 1)

Nuclei with high proton to neutron ratios

What is gamma emission?

Molecule is excited gets rid of energy to remain in ground state

Mass and atomic number do not change

Nuclei in excited state

Accompanies most nuclear reactions

What is a half-life?

Time it takes for a substance to decay to half original amount

Can back-calculate age

Longer ones have safer decay processes

Need to pass 10 half lives to be considered safe

What are nuclear reactions like energetically?

Exothermic (decay, fission, fusion, etc. are all)

What is the formula for nuclear reaction energy?

delta E = BEparent - BEdaughter

BE is binding energy holding nucleus together