Chemistry Honors: Investigation 15*

What is oxidation?

the loss of an electron by a reactant in a chemical reaction

What is reduction?

the gain of an electron by a reactant in a chemical reaction

What is a redox reaction (Oxidation-reduction reaction)

any chemical reaction that involves transferring electrons from one atom to another

What is a reducing agent?

a reactant that gives up one or more electrons in a redox reaction

What is an oxidizing agent?

a reactant that gains one or more electrons in a redox reaction

The oxidizing agent is the species that is…

reduces

The reducing agent is the species that is…

oxidized.

What are some examples of the transfer of electrons in reactions?

In ionic compounds, complete electron transfer occurs through ionic bonding; in molecular compounds, electrons are shared in covalent bonds

How is the electron transfer in polar covalent bonds?

Atoms can be considered as oxidized or reduced because the bonding electrons are pulled closer to the more electronegative atom.

How is electronegativity and electrons related?

the more electronegative atom undergoes a partial gain of electrons, so it is the oxidizing agent; the less electronegative atom undergoes a partial loss of electrons, so it is the reducing agent.

What is the oxidation number?

a positive or negative number assigned to a species to indicate its degree of oxidation or reduction; also called the oxidation state.

Positive oxidation numbers indicate…

oxidized species

Negative oxidation numbers indicate…

reduced species

Since electrons are not created or destroyed in reactions…what does that mean?

It means that mass is conserved, and any electron lost by one species must be gained by another

What are some general rules of oxidation numbers for other elements?

• Element Rule- in an uncombined element, the oxidation number of every atom is 0

• Sum Rule- in any neutral compound, the sum of all the oxidation numbers is 0

• Ion Rule- in a polyatomic ion, the sum of all the oxidation number equals the charge of the ion

What are some examples of redox reactions?

single replacement, combustion, and many combination and decomposition reactions

What are some examples of non-redox reactions

neutralization and precipitation

What is a half-reaction?

just the oxidation or reduction component of a redox reaction

How are half-reactions determined?

from the change in oxidation number of the substances.

When identifying redox reactions, what do you look for?

you look for changes in oxidation numbers or atoms in the reaction

What is the trend for the activity series of metals?

any metal that is above another metal in the activity series is more reactive and more readily oxidized.

What is the trend for metals in single replacement reactions?

The more-reactive metal replaces the less-reactive metal.

Due to conservation of mass, the total number of electrons gained in reduction must…

equal the total number of electrons lost in oxidation

What is the oxidation-number-change method?

a method of balancing a redox chemical equation by comparing the increase and decrease in oxidation numbers

What is the half-reaction method?

a method of balancing a redox reaction by first balancing its separate half-reaction equation and then combining them into a balanced redox equation

What is electric potential?

the electric potential energy divided by the charge;electric potential is measured in units of volts or joules/coulomb

What is an electrochemical process?

is any conversion between chemical potential energy and electrical energy

What is electrochemical cell?

any device that converts chemical energy into electrical energy or vice-versa; where redox reactions occur.

What is a voltaic cell?

an electrochemical cell used to convert chemical energy into electrical energy

What is a half-cell?

one part of a voltaic cell in which either oxidation or reduction takes place.

What is electrode?

a conductor in a circuit that carries electrons?

What is the anode?

the electrode at which oxidation occurs

What is the cathode?

the electrode at which reduction occurs

What is the electric potential of a voltaic cell?

is a measure of the cell’s ability to produce an electric current

The half-cell that has the greater tendency to acquire electrons…

is where reduction occurs

What is the reduction potential?

is a measure of a half-reaction’s tendency to occur as a reduction or gain of electrons.

What is the oxidation potential?

is a measure of a half-reaction’s tendency to occur as an oxidation or loss of electrons.

What is the standard reduction potential?

the reduction potential of a half-cell measured with respect to a standard hydrogen electrode

What is the standard cell potential?

the measured cell potential when the ion concentrations in the half-cells are 1M and at a temperature of 25 C and a pressure of 100 kpA

What is the formula for standard cell potential?

E^o_cell=E^o _red-E^o _oxid

What is electrolytic cell?

is an electrochemical cell that causes a chemical change through the application of electrical energy.

What does the sign of cell potential indicate?

Whether or not the reaction is thermodynamically favorable, meaning whether or not it occurs spontaneously, and therefore whether the cell is voltaic cell or an electrolytic cell.

If a voltaic cell’s cell potential is positive…

the reaction is thermodynamically favorable

If an electrolytic cell’s cell potential is negative…

the reaction is thermodynamically unfavorable

What is electrolysis?

a process by which electrical energy is used to bring about a chemical change.

What is a fuel cell?

is a type of voltaic cell in which a fuel undergoes oxidation and from which electrical energy is continuously obtained.

How to asses Redox problems?

• Assign the oxidation numbers for each elemet

• Identify the elements being oxidized and reduced

• Identify the oxidizing and reducing agent

• Balance the equation