Ch 12- Electrochemistry

Question 1

“are contained systems in which oxidation–reduction reactions occur.”

Answer 1

Electrochemical cells

Question 2

“There are three fundamental types of electrochemical cells:

Answer 2

galvanic cells (also known as voltaic cells), electrolytic cells, and concentration cells.”

“Galvanic cells and concentration cells house spontaneous reactions, whereas electrolytic cells contain nonspontaneous reactions”

Question 3

“All three types contain electrodes where oxidation and reduction take place. For all electrochemical cells, the electrode where oxidation occurs is called the ______, and the electrode where reduction occurs is called the ______.”

Answer 3

Anode, Cathode

“Other descriptors of electrochemical cells include the electromotive force (emf), which corresponds to the voltage or electrical potential difference of the cell”

Question 4

“If the emf is positive, the cell is able to release energy (ΔG 0), which means it is ______.”

Answer 4

Spontaneous, Non spontaneous

Opposite of G

“we can also state that, for all electrochemical cells, the movement of electrons is from anode to cathode, and the current (I) runs from cathode to anode. ”

Question 5

“we can also state that, for all electrochemical cells, the movement of ______ is from anode to cathode, and the ______ runs from cathode to anode. ”

Answer 5

electrons; the current (I)

Question 6

“Electrons move through an electrochemical cell opposite to

Answer 6

the flow of current (I).”

The flow of current is the flow of + charges as in conventional physics

Question 7

“Last, it is important to note that all batteries are influenced by ________ For instance, lead–acid batteries in cars, like most galvanic cells, tend to fail most in cold weather.

Answer 7

temperature changes.

Question 8

What 2 factors account for the relatively short lifespan of the galvanic cell.”

Answer 8

As mentioned earlier, the anions (Cl–) flow externally from the salt bridge into the ZnSO4, and the cations (K+) flow externally from the salt bridge into the CuSO4. This flow depletes the salt bridge and, along with the finite quantity of Cu2+ in the solution,

Question 9

“A cell diagram for the Daniell cell is as follows:

Zn (s) | Zn2+ (1 M) || Cu2+ (1 M) | Cu (s)
”

What are each parts and what do they represent

Answer 9

“The following rules are used in constructing a cell diagram:

1. The reactants and products are always listed from left to right in this form: anode | anode sol’n (concentration) || cathode sol’n (concentration) | cathode
2. A single vertical line indicates a phase boundary.
3. A double vertical line indicates the presence of a salt bridge or some other type of barrier.”

Question 10

“All types of electrochemical cells have what 3 parts regardless of which.

Answer 10

1. a reduction reaction occurring at the cathode, an oxidation reaction occurring at the anode
2. a current flowing from cathode to anode,
3. electron flow from anode to cathode.”

Question 11

What is the difference in spontaneity between the galvanic and electrolytic cell?

Answer 11

“Whereas galvanic cells house spontaneous oxidation–reduction reactions, which generate electrical energy, electrolytic cells house nonspontaneous reactions, which require the input of energy to proceed. ”

“This type of oxidation–reduction reaction driven by an external voltage source is called electrolysis, in which chemical compounds are decomposed. ”

Question 12

The electrode in an electrolytic cell (anode or cathode) can consist of what material

Answer 12

Any material, so long as it can resist the high temperatures and corrosion of the process.”

“Because electrolysis is nonspontaneous

Question 13

“was the first to define certain quantitative principles governing the behavior of electrolytic cells.”

Answer 13

Michael Faraday

“He theorized that the amount of chemical change induced in an electrolytic cell is directly proportional to the number of moles of electrons that are exchanged during the oxidation–reduction reaction. The number of moles exchanged can be determined from the balanced half-reaction.

Question 14

What is faradays law

Answer 14

“Faraday’s laws state that the liberation of gas, and deposition of elements, on electrodes is directly proportional to the number of electrons being transferred during the oxidation–reduction reaction. Here, normality or gram equivalent weight is used. These observations are proxy measurements of the amount of current flowing in a circuit.”

Question 15

What is the Faraday constant, and one faraday (F) ?

Answer 15

is equivalent to the amount of charge contained in one mole of electrons (1 F = 96,485 C) or one equivalent.”

“One electron carries a charge of 1.6 × 10–19 coulombs (C). The charge carried by one mole of electrons can be calculated by multiplying this number by Avogadro’s number,”

This is one Farad

Question 16

What is the electrodeposition equation and what is it used for?

Answer 16

mol M= It/nF

Used to determine the number of moles of element being deposited on a plate”

“where mol M is the amount of metal ion being deposited at a specific electrode, I is current, t is time, n is the number of electron equivalents for a specific metal ion, and F is the Faraday constant.”

Question 17

What is the difference between a galvanic cell and a concentration cell?

Answer 17

The distinguishing characteristic of a concentration cell is in its design: the electrodes are chemically identical.

“For example, if both electrodes are copper metal, they have the same reduction potential. Therefore, current is generated as a function of a concentration gradient established between the two solutions surrounding the electrodes.”

Question 18

“The current will stop when what happens in a concentration cell?

Answer 18

the concentrations of ionic species in the half-cells are equal. This implies that the voltage (V) or electromotive force of a concentration cell is zero when the concentrations are equal; the voltage, as a function of concentrations, can be calculated using the Nernst equation.”

Question 19

The cell membrane is an example of what type of cell?

Answer 19

Concentration cell

“he electrochemical gradient created by separation of ions across the cell membrane is analogous to a cell with two electrodes composed of the same material.”

Question 20

A rechargeable battery or cell is what

Answer 20

“is one that can function as both a galvanic and electrolytic cell.”

Question 21

“A lead–acid battery, also known as a lead storage battery, is a specific type of what

Answer 21

rechargeable battery.”

“A rechargeable cell or rechargeable battery is one that can function as both a galvanic and electrolytic cell.”

Question 22

A lead-acid battery when fully charged consists of what and when fully discharged consists of what

Answer 22

“As a voltaic cell, when fully charged, it consists of two half-cells—a Pb anode and a porous PbO2 cathode, connected by a conductive material (concentrated 4 M H2SO4).”

“ When fully discharged, it consists of two PbSO4 electroplated lead electrodes with a dilute concentration of H2SO4”

Question 23

What is Energy density

Answer 23

is a measure of a battery’s ability to produce power as a function of its weight.

“Lead–acid batteries, as compared to other cells, have some of the lowest energy-to-weight ratios (otherwise known as energy density).”

Question 24

What are two types of rechargeable batteries described in kaplan?

Answer 24

Lead Acid Batteries and Nickel-Cadmium Batteries

Question 25

“Ni–Cd batteries have a higher _________ than lead–acid batteries. The electrochemistry of the Ni–Cd half-reactions also tends to provide higher surge current.

Answer 25

energy density

Surge currents are periods of large current (amperage) early in the discharge cycle. This is preferable in appliances such as remote controls that demand rapid responses.”

Question 26

“Because the anode of a galvanic cell is the source of electrons, it is considered the _____ electrode; the cathode is considered the _____ electrode,”

Answer 26

-,+

“Electrons, therefore, move from negative (low electrical potential) to positive (high electrical potential), while the current—the flow of positive charge—is from positive (high electrical potential) to negative (low electrical potential).”

“Conversely, the anode of an electrolytic cell is considered positive because it is attached to the positive pole of the external voltage source and attracts anions from the solution. The cathode of an electrolytic cell is considered negative because it is attached to the negative pole of the external voltage source and attracts cations from the solution.”

Question 27

“Conversely, the anode of an _______ is considered positive because it is attached to the positive pole of the external voltage source and attracts anions from the solution. The cathode of an electrolytic cell is considered negative because it is attached to the negative pole of the external voltage source and attracts cations from the solution.”

Answer 27

Electrolytic Cell

Question 28

“In a _______ cell, the anode is negative and the cathode is positive. In an _______ cell, the anode is positive and the cathode is negative.

Answer 28

Galvanic; Electrolytic

This is because an external source is used to reverse the charge of an electrolytic cell. However, in both types of cells, reduction occurs at the cathode, and oxidation occurs at the anode; cations are attracted to the cathode, and anions are attracted to the anode.”

“note that—regardless of its charge designation—the cathode always attracts cations and the anode always attracts anions. ”

Question 29

“In the Daniell cell, for example, the electrons created at the anode by the oxidation of elemental zinc travel through the wire to the copper half-cell. There, they attract copper(II) cations to the cathode, resulting in the reduction of the copper ions to elemental copper, and drawing cations out of the salt bridge into the compartment. The anode, having lost electrons, attracts _____ from the salt bridge at the same time that zinc(II) ions formed by the oxidation process dissolve away from the anode.”

Answer 29

Anions

Question 30

“Anions are attracted to the _____. Cations are attracted to the _____. This is true regardless of the type of cell (galvanic, electrolytic, or concentration cells).”

Answer 30

Anode; Cathode

Question 31

“Each species has its own intrinsic reduction potential; the more positive the potential,

Answer 31

the greater the tendency to be reduced.”

“A reduction potential is measured in volts (V) and defined relative to the standard hydrogen electrode (SHE), which is given a potential of 0 V by convention. The species in a reaction that will be oxidized or reduced can be determined from the reduction potential of each species, defined as the tendency of a species to gain electrons and to be reduced. ”

Question 32

“Standard reduction potential (E°red) is measured under what conditions

Answer 32

standard conditions: 25°C (298 K), 1 atm pressure, and 1 M concentrations.

The relative reactivities of different half-cells can be compared to predict the direction of electron flow. A more positive E°red means a greater relative tendency for reduction to occur, while a less positive E°red means a greater relative tendency for oxidation to occur.”

Question 33

The relative reactivities of different half-cells can be compared to predict the direction of electron flow. A more positive E°red means what while a less positive means what

Answer 33

A more positive E°red means a greater relative tendency for reduction to occur, while a less positive E°red means a greater relative tendency for oxidation to occur.”

“A reduction potential is exactly what it sounds like. It tells us how likely a compound is to be reduced.”

Question 34

“For galvanic cells, the electrode with the more positive reduction potential is the______, and the electrode with the less positive reduction potential is the ______.”

Answer 34

Cathode; Anode

Question 35

What is the standard electromotive force (emf) or E°cell of a reaction?

Answer 35

“is the difference in potential (voltage) between two half-cells under standard conditions. The emf of a reaction is determined by calculating the difference in reduction potentials between the two half-cells:

E°cell = E°red,cathode − E°red,anode”

“When subtracting standard potentials, do not multiply them by the number of moles oxidized or reduced. This is because the potential of each electrode does not depend on the size of the electrode (the amount of material), but rather the identity of the material. The standard reduction potential of an electrode will not change unless the chemical identity of that electrode is changed.”

Question 36

“Given that the standard reduction potentials for Sm3+ and [RhCl6]3– are –2.41 V and +0.44 V, respectively, calculate the electromotive force of the following reaction:

[Sm3+] + Rh + 6 Cl– → [RhCl6]3– + Sm”

Answer 36

“First, determine the oxidation and reduction half-reactions. As written, the Rh is oxidized, and the Sm3+ is reduced:”

“Using the equation provided, the emf can be calculated as: –2.41 V – (+0.44 V) = –2.85 V. The cell is thus electrolytic. From this result, it is clear that the reaction would instead proceed spontaneously to the left, in which case the Sm would be oxidized while [RhCl6]3– would be reduced with an emf of +2.85 V.”

Question 37

“In an electrochemical cell, the work done is dependent on the number of coulombs of charge transferred and the energy available. Thus, ΔG° and emf are related as”

Answer 37

ΔG° = –nFE°cell

“where ΔG° is the standard change in free energy, n is the number of moles of electrons exchanged, F is the Faraday constant, and E°cell is the standard emf of the cell. Keep in mind that, if the Faraday constant is expressed in coulombs then ΔG° must be expressed in J, not kJ. ”

Question 38

In electrochemistry What is the similarity of this relationship to that expressed in the physics formula W = qΔV for the amount of work available or needed in the transport of a charge q across a potential difference

Answer 38

From the equation

ΔG° = –nFE°cell

ΔV: n × F is
“a charge, and E°cell is a voltage”

“Note the significance of the negative sign on the right side of the equation. ΔG° and E°cell will always have opposite signs. Therefore, galvanic cells have negative ΔG° and positive E°cell values; electrolytic cells have positive ΔG° and negative E°cell values.”

Question 39

“Concentration and the emf of a cell are related: emf varies with the changing concentrations of the species in the cell. When conditions deviate from standard conditions, one can use the Nernst equation: This is

Answer 39

Ecell=E°cell - RT(lnQ)/nF)

“where Ecell is the emf of the cell under nonstandard conditions, E°cell is the emf of the cell under standard conditions, R is the ideal gas constant, T is the temperature in kelvin, n is the number of moles of electrons, F is the Faraday constant, and Q is the reaction quotient for the reaction at a given point in time.”

“If the Nernst equation is needed on Test Day, stick with the log10 version because natural logarithm calculations get very tedious.”

“This simplified version of the equation brings together R, T (298 K), and F, and converts the natural logarithm to the base-ten logarithm to make calculations easier.”

Ecell=E°cell - 0.0592(logQ)/n

Question 40

“Combine the two expressions that solve for standard free energy change”

Answer 40

“ΔG° = –nFE°cell = –RT ln Keq”

“nFE°cell = RT ln Keq”

Question 41

“Whether it is log or ln, remember that a logarithm will be positive when equilibrium constants are ____, negative when equilibrium constants are ______, and 0 when equilibrium constants are

Answer 41

greater than 1; less than 1; equal to 1.”

Question 42

“Analysis of the equations shows us that, for redox reactions with equilibrium constants less than 1 (equilibrium state favors the reactants), the E°cell will be _______ because the natural logarithm of any number between 0 and 1 is negative.

Answer 42

Negative

These properties are characteristic of electrolytic cells, which house nonspontaneous oxidation–reduction reactions. ”

“Instead, if the equilibrium constant for the reaction is greater than 1 (equilibrium state favors the products), the E°cell will be positive because the natural logarithm of any number greater than 1 is positive. ”“These properties are characteristic of galvanic cells (spontaneous)

“If the equilibrium constant is equal to 1 (concentrations of the reactants and products are equal at equilibrium), the E°cell will be equal to zero”

Question 43

“Instead, if the equilibrium constant for the reaction is greater than 1 (equilibrium state favors the products), the E°cell will be _______ because the natural logarithm of any number greater than 1 is positive. ”

Answer 43

Positive“

These properties are characteristic of galvanic cells (spontaneous)

“If the equilibrium constant is equal to 1 (concentrations of the reactants and products are equal at equilibrium), the E°cell will be equal to zero”

Question 44

“If the equilibrium constant is equal to 1 (concentrations of the reactants and products are equal at equilibrium), the E°cell will be equal to

Answer 44

zero!

“An easy way to remember this is that E°cell = 0 V for any concentration cell with equimolar concentrations in both half-cells because there is no net ionic equation (both half-cells contain the same ions).

Question 45

“If E°cell is positive, ln Keq is positive. This means that Keq must be greater than one and that the equilibrium lies to the

Answer 45

right (products are favored).”

Question 46

“Certain characteristics are shared between all types of electrochemical cells.”

Answer 46

“Electrodes are strips of metal or other conductive materials placed in an electrolyte solution.
The anode is always the site of oxidation. It attracts anions.
The cathode is always the site of reduction. It attracts cations.
Electrons flow from the anode to the cathode.
Current flows from the cathode to the anode.”

Question 47

What are cell diagrams and how are they written?

Answer 47

“Cell diagrams are shorthand notation that represent the reactions taking place in an electrochemical cell.

“Cell diagrams are written from anode to cathode with electrolytes (the solution) in between.
A vertical line represents a phase boundary, and a double vertical line represents a salt bridge or other physical boundary.”

Question 48

“house spontaneous reactions (ΔG

Answer 48

Galvanic (voltaic) cells

Question 49

House nonspontaneous reactions (ΔG > 0) with a negative electromotive force. These nonspontaneous cells can be used to create useful products through electrolysis.”

Answer 49

“Electrolytic cells

Question 50

are a specialized form of a galvanic cell in which both electrodes are made of the same material. Rather than a potential difference causing the movement of charge, it is the concentration gradient between the two solutions.”

Answer 50

“Concentration cells

Question 51

How is the charge on an electrode dependent on the type of electrochemical cell one is studying

Answer 51

• For galvanic cells, the anode is negatively charged and the cathode is positively charged.
• For electrolytic cells, the anode is positively charged and the cathode is negatively charged.”

Question 52

“are electrochemical cells that can experience charging (electrolytic) and discharging (galvanic) states. Rechargeable batteries are often ranked by energy density—the amount of energy a cell can produce relative to the mass of battery material.”

Answer 52

Rechargeable Batteries

Question 53

“when discharging, consist of a Pb anode and a PbO2 cathode in a concentrated sulfuric acid solution. When charging, the PbSO4-plated electrodes are dissociated to restore the original Pb and PbO2 electrodes and concentrate the electrolyte. These cells have a low energy density.”

Answer 53

Lead-Acid Batteries

Question 54

“when discharging, consist of a Cd anode and a NiO(OH) cathode in a concentrated KOH solution. When charging, the Ni(OH)2- and Cd(OH)2-plated electrodes are dissociated to restore the original Cd and NiO(OH) electrodes and concentrate the electrolyte. These cells have a higher energy density than lead–acid batteries.”

Answer 54

“Nickel–cadmium batteries (Ni–Cd)”

Question 55

“batteries have more or less replaced Ni–Cd batteries because they have higher energy density, are more cost effective, and are significantly less toxic.”

Answer 55

“Nickel–metal hydride (NiMH)”

Question 56

These batteries have more or less replaced Ni–Cd batteries because they have higher energy density, are more cost effective, and are significantly less toxic.

Answer 56

“Nickel–metal hydride (NiMH)”

Question 57

“is an above-average current transiently released at the beginning of the discharge phase; it wanes rapidly until a stable current is achieved.”

Answer 57

Surge Current

Question 58

“quantifies the tendency for a species to gain electrons and be reduced. The higher the reduction potential, the more a given species wants to be reduced.”

Answer 58

Reduction Potential

Question 59

“are calculated by comparison to the standard hydrogen electrode (SHE) under the standard conditions of 298 K, 1 atm pressure, and 1 M concentrations.”

Answer 59

“Standard reduction potentials (E°red”

“The standard hydrogen electrode has a standard reduction potential of 0 V.”

Question 60

“ is the difference in standard reduction potential between the two half-cells.”

Answer 60

“Standard electromotive force (E°cell)”

“For galvanic cells, the difference of the reduction potentials of the two half-reactions is positive; for electrolytic cells, the difference of the reduction potentials of the two half-reactions is negative”

Question 61

“For galvanic cells, the difference of the reduction potentials of the two half-reactions is _____; for electrolytic cells, the difference of the reduction potentials of the two half-reactions is ______”

Answer 61

Positive; Negative

Question 62

“Electromotive force and change in free energy always have ______ signs.

Answer 62

Opposite

When E°cell is positive, ΔG° is negative. This is the case in galvanic cells.
When E°cell is negative, ΔG° is positive. This is the case in electrolytic cells.
When E°cell is 0, ΔG° is 0. This is the case in concentration cells.”

Question 63

“The ________ describes the relationship between the concentration of species in a solution under nonstandard conditions and the electromotive force.”

Answer 63

Nernst equation

Question 64

“There exists a relationship between the equilibrium constant (Keq) and E°cell

What are they

Answer 64

“When Keq (the ratio of products’ concentrations at equilibrium over reactants’, raised to their stoichiometric coefficients) is greater than 1, E°cell is positive.
When Keq is less than 1, E°cell is negative.
When Keq is equal to 1, E°cell is 0.”