1. Electrochemical & Voltaic Cells
Notes: (21.1)
An electrochemical cell is a device that either changes chemical energy to electrical energy or electrical energy into chemical energy. The change in driven by oxidation/reduction reactions (redox) which follows the activity series of metals.

2. Voltage Voltage is the measure of energy available to move electrons.
Sometimes called potential difference (electrical PE)
Measured in volts (V) (1Joule/coulomb)
The higher the voltage, the more energy each electron carries
In order for there to be voltage there must be a continuous replacement of charge. (battery, power plant, electrochemical cell)

3. Voltaic Cells
A voltaic cell operates as redox reactions spontaneously occur between two different materials (usually metals).
Provides a steady electric current from chemical energy.
the reaction is driven by the cell (electron) potential
the difference in the amount of electrons (charge) within each cell connected by a conductor
measured in volts (V)
voltage is the measure of the potential size or force of the charge (also known as potential difference)
can be determined by the difference in the half-cell reduction potentials

4. Voltaic Cells – Reduction Potential
can be determined by the difference in the half-cell reduction potentials
measured at standard conditions; 1M, 25oC, and 1 atm
anode (oxidation ) is represented by a negative number
electrons are produced - charge on the element becomes more positive
Zn(s) g Zn2+(aq)+ 2e-
cathode (reduction ) is represented by a positive number
electrons are consumed
charge on the element becomes more positive
Cu2+(aq) + 2e- g Cu(s)
the greater the absolute value between the two potentials, the greater the voltage that is generated
0.35 – (-0.76) = 1.1V

5. Half Cell Reactions Anode Cathode
The zinc is broken (oxidized) down to release ions (Zn2+) in the electrolyte solution (ZnSO4)
Zn(s) g Zn2+(aq) + 2e-
Cathode
The copper is built up (reduced) absorbing ions from the electrolyte solution (CuSO4)
Cu2+(aq) + 2e- g Cu(s)
Each ½ cell is connected through a conductor
The excess electrons then flow from the anode (negative zinc terminal) through the conductor to the cathode (positive copper terminal) and then back through the electrolyte solution to the zinc terminal.
The salt bridge is created to separate the two metals
differentially allows ions and electrons to travel from one compartment to another while keeping the metals separate
separates the two half-cells of the battery
each half-cell contains ~ the same ratio of + & - ions as long as the circuit is connected