Introduction to Electrochemistry

Electrochemistry

study of the interchange between chemical change and electrical work

Electrochemical cells

systems utilizing a redox reaction to produce or use electrical energy

Redox reactions

electron transfer processes

oxidation

loss of 1 or more e^-

reduction

gain of 1 or more e^-

oxidation numbers

imaginary charges

Pure element oxidation number

zero

monatomic ion oxidation number

is charge

neutral compound oxidation number

sum of O. N. is zero

polyatomic ion oxidation number

sum of O. N. is ion’s charge

Negative O. N is generally assigned to…

more electronegative element

hydrogen O.N.

assigned +1 (metal hydrides, -1)

oxygen O. N.

assigned -2

Fluorine O. N.

always -1

What happens to O.N. when oxidized?

O.N. increases (more positive)

What happens to O.N. during reduction?

O.N decreases (more negative)

oxidation causes…

reduction (reducing agent)

reduction causes…

oxidation (oxidizing agent)

Redox reaction involves transfer of…

electrons from one species to another chemicals are separated

You can monitor redox reaction when…

electrons flow through an electric current

electric current is proportional…

to rate of reaction

cell voltage is proportional to…

free-energy change

where does oxidation occur?

Anode

Where are electrons produced?

anode

What do anions migrate toward?

Anode

What has a negative sign

Anode

Where does reduction occur?

Cathode

Where are electrons consumed?

Cathode

What do cations migrate toward?

Cathode

What has a positive sign?

Cathode

A redox titration is an analytical technique base on..

the transfer of electrons between analyte and titrant

A substance is reduced when it…

gains electrons from another substance

gain of e^- net decrease in…

charge of species; oxidizing agent (oxidant)

A substance is oxidized when it…

loses electrons to another substance

loss of e^- net increase in…

charge of species; reducing agent (reductant)

The net reaction is known as the total…

cell reaction

In order for a redox reaction to occur, both reduction of one compound and…

oxidation of another must take place simultaneously

Total number of electrons is….

constant in a redox reaction

Oxidation number

a positive or negative number assigned to an atom to indicate its degree of oxidation or reduction

Generally, a bonded atom’s oxidation number is the charge it…

would have if the electrons in the bond were assigned to the atom of the more electronegative element

The oxidation number of any uncombined…

element is zero

The oxidation number of a monatomic ion…

equals its charged

The sum of the oxidation numbers of the atoms…

in the compound must equal 0

The sum of the oxidation numbers in the formula of a polyatomic ion…

is equal to its ionic charge

The metals in Group 1A have an

oxidation number of +1

The elements in group IIA have an

oxidation number of +2

The elements in Group VIIA often form…

compounds that have a -1 oxidation number

An increase in oxidation number is

considered oxidation

A decrease in oxidation number is

considered reduction

Active metals are strong reducing agents because…

• they are easily oxidized

• they are strong reducing agents

Active nonmetals are strong oxidizing agents because

• they are easily reduced

• they gain electrons easily