Chemistry Chapter 16: Electrochemistry

Oxidation-reduction (redox) reactions

Reactions involving a change in oxidation number for one or more reactant elements

Oxidation

Losing electrons

Reduction

Gaining electrons

Oxidation agent

Oxidizes something else; is reduced itself

Reduction agent

Reduces something else; is oxidized itself

Oxidation rule of elemental substances

Have an oxidation state of 0

Oxidation rule of monoatomic substances

Have an oxidation state equal th the charge

Oxidation rule for neutral molecules

Sum of oxidation states adds up to 0

Oxidation rule for polyatomic ions

Sum of oxidation states add up to the charge

Oxidation rule for group 1A metals and H in compounds

Have an oxidation state of 1

Oxidation rule for group 2A metals in compounds

Have an oxidation state of 2

Oxidation rule for Oxygen

Have an oxidation state of -2

Oxidation rule for Fluorine

Have an oxidation state of -1

First step in balancing redox reactions

Determine the oxidation states of all atoms and identify the reactants being oxidized and reduced

Second step in balancing redox reactions

Split the overall reaction into two half-reactions

Third step in balancing redox reactions

Balance each half-reaction using mass, beginning with all elements other than H and O, then balancing O with H2O, and then balancing H with H⁺

Balancing basic redox reactions

Neutralize H⁺ by adding one OH^- for each H⁺, to both sides

Fourth step in balancing redox reactions

Balance each half-reactions’ charge by adding electrons

Fifth step in balancing redox reactions

Make the number of electrons in both half-reactions equal by multiplying one (or both) half-reactions by a small integer

Sixth step in balancing redox reactions

Add the two half-reactions together

Seventh step in balancing redox reactions

Verify that both mass and charge are balanced

Voltaic (galvanic) cell

An electrochemical cell in which spontaneous redox reactions produce electrical energy

Half-cell

One half of an electrochemical cell where either oxidation or reduction occurs

Electrolyte

A substance that dissolves in water to form solutions that conduct electricity

Electrode

Conductive surfaces through which electrons can enter or leave the half-cells

Anode

The electrode where oxidation occurs

Cathode

The electrode where reduction occurs

Salt bridge

A u-shaped tube containing a strong electrolyte to complete the circuit by flowing ions to neutralize the charge build-up in half-cells

Electrolytic cell

An electrochemical cell that consumes electrical currents to drive a nonspontaneous chemical reaction

Electrochemical cell notation

Anode|Electrolyte||Electrolyte|Cathode

Cell potential

The driving force for the flow of electrons from the anode toward the cathode.

Standard cell potential

Cell potential at standard conditions; always refers to the half-reaction written as a reduction

Cell potential of voltaic cells

E>0

Cell potential for electrolytic cells

E<0

Electrolysis

The process by which electrical current is used to drive a nonspontaneous reaction

Ampere (A)

A measure of current that describes the flow of electrons per second