Chemistry Unit Four

Relationship Between Electricity and a Chemical Reaction

1. Chemical reactions create electricity

2. Electricity makes chemical reactions happen or not

Electricity

movement of electrons through a medium

Oxidation

lose electrons, increase oxidation number, species oxidized is the reducing agent, (sometimes) increases in oxygen

Reduction

gain electrons, reduction in oxidation number, species reduced is the oxidizing agent, (sometimes) decrease in oxygen

Oxidation Number

The charge an atom would have in a molecule if electrons were completely transferred

Oxidation Number Rules

1. All elements in their standard state have oxidation numbers equal to zero

2. The oxidation number of a monatomic ion is its charge

3. Hydrogen oxidation number is +1 except when bonded to metals. ex. NaH

4. Oxygen oxidation number is usually -2, except in peroxides oxygen is -1

5. The sum of the oxidation numbers of all the atoms in a molecule or ion is equal to the charge.

Steps to balance a redox reaction using the half-reaction method

1. Write skeletal equations for the oxidation and reduction half-reactions.
2. Balance each half-reaction for all elements except H and O.
3. Balance each half-reaction for O by adding H2O.
4. Balance each half-reaction for H by adding H+.
5. Balance each half-reaction for charge by adding electrons.
6. If necessary, multiply one or both half-reactions so that the number of electrons
consumed in one is equal to the number produced in the other.
7. Add the two half-reactions and simplify.
8. If the reaction takes place in a basic medium, add OH− ions to the equation obtained in
step 7 to neutralize the H+ ions (add in equal numbers to both sides of the equation) and
simplify.

Galvanic Cell

a device used to generate electricity using the spontaneous transfer of electrons; spontaneous redox reaction

battery

a group of galvanic cells wired together in series for direct conversion of chemical energy to electrical energy

anode

oxidation happens at which part of the galvanic cell?

cathode

reduction occurs at which part of the galvanic cell

cell voltage, cell potential, and electromotive force

The difference in electrical potential between the anode and cathode is called

Standard Reduction Potential

the voltage associated with a reduction reaction at an electrode when all solutes are at standard conditions

the greater the tendency for the substance to be reduced

The more postivie Edegree =

the greater the tendency for the substance to be oxidized

the more negative Edegree

the reaction is reversed

the sign of E degree

does not change the value of Edegree

Changing the stoichiometric coeffcients of a half-cell reaction

Edegree cathode- Edegree anode

Edegree of cell=

Spontaneous

Edegree >0

nonspontaneous

Edegree< 0

Primary Batteries

not rechargeable

Secondary Batteries

Rechargeable

Proton exchange-membrane Fuel Cell

a galvanic cell that produces electricity by converting the chemical energy of a fuel directly into electricity; reactants must be continuously supplied; H2 and O2 are the fuels

Corrosion of Iron

requires both oxygen and water; salt accelerates corrosion by increasing the conductivity of water.

Ways to Protect against Corrosion

1. Galvanization Coating a metal with Zn; Zn is a sacrifical anode

2. Painting or other coating

3. Cathodic Protection

Cathodic Protection

sacrifical anodes will degrade over time and can be replaced; the cathode acts to conduct electrons and is not consumed in a reaction.

Cathodic Protection Example

connecting iron storage tanks (cathode) to a stronger reducing agen like Mg or Zn (sacrifical anode)

Electrolysis

the process in which electrical energy is used to cause a nonspontaneous chemical reaction to occur.

organic chemistry

the study of the classification and synthesis of carbon-containing compounds

Alkanes

single carbon to carbon bonds

Alkenes

double carbon to carbon bonds

Alkynes

triple carbon to carbon bonds

aromatic

based on benzene

hydrocarbons

compounds of only C and H

Unsaturated

organic compounds that contain carbon-carbon double and triple bonds

Cycloalkanes

represented by polygons

Steps for naming brandched hydrocarbons

1. name the longest continous carbon chain, include any double or triple bond in the chain

2. Number the branches so they get the lowest possible prefixes

3. Add location and name of branches alphabetically to the parent chain

Isomers

have identical composition but different structures

Structural/Constitutional isomers

compounds with the same molecular formula but different connectivity of atoms

Geometric Isomers

compounds with the same connectivity but different spatial arrangement due to restricted rotation