Unit 4- Electrochemistry

Question 1

Define Redox Reactions

Answer 1

Reactions that involve the transfer of electrons from one reactant to another.

Question 2

Define Oxidation Number

Answer 2

The charge the atom would take if all shared electrons in a compound were assigned to the atom with the greatest attraction for those electrons.

Question 3

Are oxidation numbers the same thing as charges? How is the notation typically implemented?

Answer 3

They are not the same thing as charges; for oxidation numbers, the sign would be to the LEFT of the number and for charges, the sign would be to the RIGHT of the number.

Question 4

What is the oxidation number of a free element?

Answer 4

0

Question 5

Define Oxidation

Answer 5

Oxidation is defined as the loss of electrons.

Question 6

Define Reduction

Answer 6

Reduction is defined as a gain of electrons.

Question 7

Define Oxidizing Agent

Answer 7

The substance that causes the oxidation of another substance; the oxidizing agent is ALWAYS REDUCED.

Question 8

Define Reducing Agent

Answer 8

A substance that causes the reduction of another substance; the reducing agent is ALWAYS OXIDIZED.

Question 9

What is Electrochemistry?

Answer 9

Reactions that involve the transfer of electrons to generate an electron current.

Question 10

Define Electrochemical Cell

Answer 10

The generation of electricity through redox reactions is carried out through using an electrochemical cell.

Question 11

Define Voltaic Cell

Answer 11

An electrochemical cell that produces electrical currents from a spontaneous reaction as electrons are transferred from one atom to another.

Question 12

Define Half-Cell

Answer 12

Placing a piece of metal in an electrolyte solution makes a half cell. A galvanic cell is composed of two half cells connected via an electrical conductor and a salt bridge.

Question 13

What happens to each side of the half-cell respectively?

Answer 13

One of the half cells goes through oxidation and the other goes through reduction.

Question 14

Define Electrical Current

Answer 14

An electrical current is the result of moving charges. It is measured in Amperes (A) which is equivalent to 1 Coulomb (C)/s

Question 15

For the anode metal, where does the ion of the metal go?

Answer 15

In the anion, the metal ion goes AWAY.

Question 16

For the cathode metal, where does the ion of the metal go?

Answer 16

The ion of the cathode metal goes TOWARDS it.

Question 17

Define Potential Difference

Answer 17

A measure of the difference in potential energy between 2 positions. It is often measured in Volts.

1V= 1J/C

Question 18

Define Electromotive Force

Answer 18

The potential difference gives rise to the force that moves electrons, which is called the electromotive force.

Question 19

Define Cell Potential

Answer 19

The potential difference between the two electrodes is called the cell potential.

Question 20

Define Salt Bridge

Answer 20

A salt bridge connects the two half cells and allows for ions to pass to ensure electrical neutrality.

Question 21

How do electrons flow from the electrodes?

Answer 21

ELECTRONS ALWAYS FLOW FROM THE ANODE TO THE CATHODE.

Question 22

Define Anode

Answer 22

The electrode where oxidation occurs. OA

Question 23

Define Cathode

Answer 23

The electrode where reduction occurs is the cathode. RC

Question 24

How is Line Notation usually done?

Answer 24

All the compounds are listed with vertical lines separating the phases and a double vertical line separating the anode and the cathode.

Question 25

What does the value of the cell potential (E Cell) depend on?

Answer 25

Concentration of reactants, temperature, and pressure.

Question 26

What does it mean when one of the electrodes has a more negative Voltage?

Answer 26

It means that it has a higher potential.

Question 27

What are the conditions for the standard hydrogen electron (SHE)?

Answer 27

0V, 1 atm for gases, 1M for reactant concentrations.

Question 28

What is the formula for the standard cell potential?

Answer 28

E Cathode- E Anode

Question 29

When you flip a reaction to measure the standard reduction potential, what are the thing that do change and DO NOT change respectively?

Answer 29

Only the sign of the E Cell would change; since it’s necessary to balance the equations to cancel out the electrons on both sides, you would need to multiply the reactions respectively. HOWEVER, you do NOT MULTIPLY THE VALUES OF THE E CELL.

Question 30

Define Standard Free Energy Change

Answer 30

The maximum amount of work that can be performed by a system.

Question 31

What is the equation for relating the Standard Free Energy and the work done by the transfer of free electrons?

Answer 31

Delta G= -nFE Cell where n=number of electrons transferred (balanced redox reaction); F= 9.6485x10^4C/mol (Faraday’s constant); E Cell= Standard Cell Potential

Question 32

Under what conditions is a reaction considered to be spontaneous?

Answer 32

When Delta G is less than 0.

Question 33

With respect to E cell, when is the reaction considered spontaneous?

Answer 33

When the E cell value is positive.

Question 34

What is the equation demonstrating the relationship between Delta G and K?

Answer 34

Delta G= -RTln K where R= 8.314J/mol and T is the absolute temperature in kelvin.

Question 35

In the equation demonstrating the relationship between free energy and K, what do the values of K tell us?

Answer 35

When K is greater than 1, the products are favored at equilibrium; when K is less than 1, the reactants are favored at equilibrium. When K=1, the products and reactants are favored equally at equilibrium.

Question 36

What is the equation demonstrating the relationship between E and K?

Answer 36

E cell= 0.0592V/n x log K ; there is a direct relationship between E AND K.

Question 37

For what values of E and K is the reaction considered spontaneous?

Answer 37

When K is greater than 1 and E is positive, the reaction is considered spontaneous.

Question 38

For what values of E and K is the reaction considered to be not spontaneous?

Answer 38

When the value of K is less than 1 and the E cell is negative, the reaction is considered to be non spontaneous.

Question 39

For what values of E and K is the reaction considered to be at equilibrium?

Answer 39

When the K is equal to 1 and the E cell is 0, the reaction is considered to be at equilibrium.

Question 40

What is the Nernst Equation and what does it allow us to do?

Answer 40

It essentially allows us to evaluate the cell potential at non standard conditions and the equation for it is:

E Cell= E Cell*- 0.0592V/n (log10 Q)

Question 41

What does the term Concentration Cell imply?

Answer 41

It means the same substance is used as the cathode and the anode at different concentrations.

Question 42

When calculating the cell potential of the concentration cell, what will be the value for E Cell* and how do we determine the value for Q?

Answer 42

The value for E Cell * will always be 0 and the way to calculate Q is to have the first concentration that appears i the line notation to be included in the numerator and the one after to appear int he denominator.

Question 43

Based off values in the standard reduction table, how can you identify the strength of an oxidizing/reducing agent?

Answer 43

The more positive it is, the stronger oxidizing agent it is; the more negative it is, the more stronger reducing agent it is.