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.

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)

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

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

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