Ch 18 Introduction to Electrochemistry Flashcards
electrons are transferred from one reactant to
another.
oxidation/reduction reaction e
A substance that has a strong affinity for electrons
oxidizing agent,
Species that donates electrons to another species.
Reducing agent
the reaction is carried out in an ____________ in which the reactants do not come in direct contact with one another.
electrochemical cell
are widely used in electrochemistry to prevent
mixing of the contents of the two electrolyte solutions making up electrochemical cells.
Salt bridges
A unique aspect of oxidation/reduction reactions is that the transfer of
electrons, and thus an identical net reaction, can often be brought about in an ____________ in which the oxidizing agent and the reducing agent are physically separated from one another
electrochemical cell
It isolates the reactants but maintains electrical contact between the
two halves of the cell
salt bridge
When a voltmeter of high internal resistance is connected as
shown or the electrodes are not connected externally, the cell is said to be at _________ and delivers the full cell potential
open circuit
A circuit where no net reaction
occurs in the cell, although we shall show that the cell has the potential for doing
work.
open circuit
The voltmeter measures the potential difference, or _________, between the two
electrodes at any instant.
voltage
is a measure of the tendency of the cell reaction to proceed toward equilibrium.
voltage
In a salt bridge, the two ends of the bridge are
fitted with ____________ to prevent liquid from siphoning from one part of the cell to
the other.
sintered glass disks/ porous materials
The equilibrium-constant
expression
Keq = oxidized/ reduced
As the reaction goes on in an electrochemical cell, the cell potential, when the circuit is open, _________ and approaches ____________
as the overall reaction approaches equilibrium.
decreases continuously , zero
The electrodes in some cells share a
common electrolyte; these are known
as
cells without liquid junction
An electrochemical cell consists of two conductors
electrodes
is an electrode where
reduction occurs.
cathode
is an electrode where oxidation occurs.
anode
Types of Electrochemical Cells
galvanic or electrolytic cells
The cell that store electrical energy
Galvanic cells
The cell that consume electricity
electrolytic cells
are usually made from galvanic cells connected in series to produce higher voltages than a single cell can produce
Batteries
Galvanic cells operate spontaneously, and the net reaction during discharge is called the
spontaneous cell reaction.
in contrast to a voltaic cell, requires an external source of
electrical energy for operation.
electrolytic cell
reversing the current reverses the cell reaction.
reversible cell
reversing the current
causes a different half-reaction to occur
at one or both of the electrodes.
irreversible cell
was one of the earliest galvanic cells to find widespread
practical application. It was used in the mid-1800s to power telegraphic communication systems.
Daniell Gravity Cell
In the shorthand notation to describe electrochemical cells, a single vertical line indicates a _________ at
which a potential develops
phase boundary
In the shorthand notation to describe electrochemical cells, the double vertical lines represent _____, one at each end of the salt bridge
two-phase
boundaries
The junction potential results from differences in the rates at which the ions in the cell compartments and the salt bridge migrate across the interfaces.
liquid-junction potential
A liquid-junction potential can amount to as much as several hundredths
of a volt but can be negligibly small if the electrolyte in the salt bridge has an anion
and a cation that migrate at nearly the same rate. A saturated solution of _____________is the electrolyte that is most widely used.
potassium
chloride, KCl
___________ carry the charge within the electrodes as well as the external conductor.
Notice that by convention, __________, which is normally indicated by the symbol I,
is opposite in direction to electron flow
Electrons, current
are the charge carriers within the cell
Anions and cations
The phase boundary between an
electrode and its solution is called an
.
interface
Equation than relates the cell potential, Ecell, to the free energy of the reaction, to the equilibrium constant
△G = -nFEcell = -RT ln Keq
The ____ of a substance is a
reference state that allows us to obtain
relative values of such thermodynamic
quantities as free energy, activity,
enthalpy, and entropy
standard state
If the reactants and products are in their standard states, the resulting cell potential
is called the
standard cell potential
This rule implies that we always measure the cell potential by connecting the positive lead of the voltmeter to the right-hand electrode in
the schematic or cell drawing
plus right rule.
The leads of voltmeters are color
coded. The__________ is red,
and the _________ is black.
positive lead, common lead
The reaction is not spontaneous cell reaction when Ecell is _________, and
△G is thus _______.
negative, positive
This generally agreed-upon reference half-cell against which all others are compared.
Such an electrode must be easy to construct, reversible, and highly reproducible in
its behavior. The universal reference electrode
standard hydrogen electrode (SHE)
The standard hydrogen electrode
is sometimes called the
normal
hydrogen electrode (NHE).
The metal conductor is a piece of platinum that has been coated, or ______________, with
finely divided platinum (platinum black) to increase its specific surface area.
platinized
______ is a layer of
finely divided platinum that
is formed on the surface of a
smooth platinum electrode
by electrolytic deposition of
the metal from a solution of
chloroplatinic acid, H2PtCl6. It provides a large
specific surface area of platinum
Platinum black
The assigned value for the potential of standard hydrogen electrode (SHE) at all temperatures
0.000 V
is defined as the potential of a cell in which the electrode
in question is the right-hand electrode and the standard hydrogen electrode is the
left-hand electrode
electrode potential
of a half-reaction is defined as its electrode
potential when the activities of the reactants and products are all unity
standard electrode potential, E^0
A metal ion/metal half-cell is
sometimes called a .
couple
An ___________is by definition
a reduction potential or the half-reactions written as reductions
relative electrode potential
An_______________is a measure of the extent to which the concentrations of the
species in a half-cell differ from their equilibrium values
electrode potential
The _______________for
a half-reaction, E^0, is defined as the
electrode potential when all reactants
and products of a half-reaction are at
unit activity.
standard electrode potential
A ______________is the electrode
potential when the ratio of analytical
concentrations of reactants and
products of a half-reaction are exactly
1.00 and the molar concentrations
of any other solutes are specified. To
distinguish the formal potential from
the standard electrode potential a
prime symbol is added to E^0’
.
formal potential
are empirical potentials that compensate for the types of activity and competing equilibria effects that we have just described.
formal potential
