Electrochemical Cells

What do electrochemical cells do?

interconvert electrical and chemical energy

Name types of cells. Name each form of the types present.

1. Primary Cells

   1. galvanic

   2. voltaic

   3. secondary (rechargeable)

   4. fuel cells

2. Electrolytic

How do Primary Cells Function?

generate electricity from spontaneous, irreversible, exothermic chemical reactions

How do Electrolytic Cells Function?

electrical energy is used to drive forward non- spontaneous, reversible, chemical reactions

What is a Battery?

two or more electrochemical cells in a single container

What is a Primary Cell?

• a device that changes chemical energy (from a redox reaction) into electrical energy

• Reaction materials will be consumed, and either the anode/electrolyte or both will need to be replaced or the battery thrown away.

• Oxidation and reduction reactions are separated into two half- cells/compartments, but are connected by an external wire to allow for electrons to flow between them

Primary Cell Components

• Each half cell has a conductor (electrode)

• The electrode where OXIDATION occurs is the anode (-)

• The electrode where REDUCTION occurs is the cathode (+)

• Each half cell is connected by a salt bridge to neutralize build-up of charges and maintain potential difference

  • anions flow from cathode → anode through salt bridge, cations from anode → cathode. NO SALT BRIDGE— NO VOLTAGE

• potential difference created when circuit is complete and can. be measured with a voltmeter

What is a Salt Bridge?

a glass tube or absorptive paper containing aqueous, non-reactive, solution of ions

What do primary cells look like?

What are Electron Potentials?

charge separation between the metal and its ions in solution within the half cells

What physically occurs in cell wrt Electron Potentials?

atoms will form ions by releasing e⁻, making the surface of the metal negative wrt the solution all while ions in the solution gain e⁻ to form atoms (equilibrium)

How is reactivity related to Electron Potentials?

The reactivity of the metal determines the magnitude of electrode potential and position of equilibrium in the half cell

RULE: more reactive metal = more negative electrode potential

What is a Cell Diagram Convention? How do you draw one?

a shorthand way to represent primary cells

1. Anode on the left, cathode on the right (e⁻ flow from left to right)

2. double vertical line represents salt bridge

3. single vertical line is phase boundary (eg. solid electrode and aqueous solution)

4. aqueous solutions of each electrode are next to the salt bridge

5. If a half-cell has two ions, separate with comma since they are in the same phase

What would a Cell Diagram Convention of Zinc and Copper look like?

How do you predict Cell Reactions?

1. You look at the two metals in the half cells

2. direction of electron flow and voltage is determined by the relative strength of the reducing agents

3. Find which metal is higher on the Activity Series

4. Whichever element is higher will oxidize (anode- stronger

   reducing agent), and the lower

   is being reduced (cathode -

   weaker reducing agent).

Draw galvanic cell using zinc and copper metal

Trick:

Red Cat

An Ox

wrt Secondary Cells, how can electricity generating reactions be reversed?

by applying current

wrt Secondary Cells, what are their pros and cons?

Pro	Con
satisfy higher current demands	have a higher rate of self-discharge

Tell me about Fuel Cells

• converts hydrogen, methanol, or ethanol and oxygen into water, carbon dioxide and heat.

• cause little pollution and are very efficient

• not rechargeable but need steady supply of fuel