DAT gen chem ch11 Redox and Electrochemistry

the study of the relationship between chemical reactions and electrical energy

Oxidation Is Loss\

of electrons

Reduction Is Gain/

causes another atom in a redox rxn to undergo oxidation and become reduced

causes another atom to reduced and become oxidized

numbers assigned to atoms in order to keep track of the redistribution of electrons during a chemical rxn

1. all free elements have ox# 0

2. monatomic ion ox# is equal to the charge of the ion

3. Group IA elements have an ox# of +1. Group IIA elements have an ox# of +2.

4. Group VIIA elements have ox# of -1 unless combined with an element of higher electronegativity

5. Hydrogen has an ox# of -1 in compounds with less electronegative elements than hydrogen. Hydrogen is more normally +1.

6. Oxygen is usually -2.

7. sum ox# of all atoms in a neutral compound is 0. Sum of ox# of all atoms in a polyatomic ion is equal to the charge of the ion.

the rxn is separated into the oxidation half-rxn and reduction half-rxn, each is balanced separately, and the two are added to give a balanced overall rxn

electrochemical cell in which the redox reaction has a negative G and is therefore a spontaneous reaction.

electrode at which oxidation occurs

electrode at which reduction occurs

galvanic cells

two half-cells, one with ZnSO4 and an zinc bar, one with CuSO4 and a copper bar connected by a wire with a voltage meter and a salt bridge

cathode- copper bar
anode- zinc bar

supply energy, used to do work

tube that contains an inert electrolyte that will not interact with the chemicals in the half-cells. used to permit exchange of cations and anions between the half-cells

zinc is oxidized to Zn^2+, sends electrons through the wire to the copper cathode. Cu^2+ ions in solution are reduced to solid copper

a shorthand notation representing the reactions in an electrochemical cell

anode| anode solution|| cathode solution | cathode

electrochemical cell in which the redox rxn has a positive G and is nonspontaneous

electrical energy is required to induce the rxn of an electrolytic cell

96,487 coulombs = 1 Faraday

oxidation and reduction half-cells are usually placed in one container

anode is positive
cathode is negative

anode is negative
cathode is positive

the tendency of a species to acquire electrons and be reduced, measured in volts

A more positive potential means likely to be reduced.

standard for assigning reduction potentials, has a potential of 0.00 V

reduction potential measured under standard conditions;: 25 degrees C, 1M concentrations of each ion participating, 1 atm of gasses participating, pure metals

the difference in potential between two half-cells

emf=E_red+E_ox

take the standard reduction potential and reverse the sign
don't forget to reverse the equation too

galvanic - positive emf

electrolytic - negative emf

G = -nFE_cell
n=mol electrons exchanged
F= Faraday's constant (in J/V)
E_cell=emf of the cell
G must be expressed in J, not kJ.

can be used under standard conditions to find standard G

E_cell = standard E_cell - (RT/nF)(lnQ)

measures the emf of a cell

type of voltmeter that gives a more accurate reading of the difference in potential between two electrodes

nF(standard E_cell)=RT(lnK_eq)

emf is positive

positive, the equilibrium lies to the products side.