Redox Reaction and Voltaic Cell PDF

Redox Reaction and Voltaic Cell Learning Objectives Define redox reaction. Interpret standard reduction potential. Discuss galvanic/voltaic cell. ▪ an electron transfer reaction ▪ coupled reaction ▪ no oxidation if there is no reduction ▪ no reduction if there...

Redox Reaction and Voltaic Cell Learning Objectives Define redox reaction. Interpret standard reduction potential. Discuss galvanic/voltaic cell. ▪ an electron transfer reaction ▪ coupled reaction ▪ no oxidation if there is no reduction ▪ no reduction if there is no oxidation LEORA: Loss of Electron Oxidation Reducing Agent GEROA: Gain of Electron Reduction Oxidizing Agent  ▪ devices that make use of the inter-conversion of electrical and chemical energy. ▪ generate electricity from ▪ make use of electricity or electric spontaneous reactions current for certain chemical reactions to occur  ▪ generate electricity from spontaneous reactions ▪ OXIDATION occurs at the anode Cu Cu2+ + 2e- LEORA ▪ Electrons produced accumulate at the anode making the anode the NEGATIVE ELECTRODE  ▪ generate electricity from spontaneous reactions ▪ ELECTRONS move from anode to cathode passing through the external wire ▪ generate electricity from spontaneous reactions ▪ REDUCTION occurs at the cathode (POSITIVE ELECTRODE) Ag+ + e- Ag GEROA  ▪ generate electricity from spontaneous reactions ▪ ELECTROMOTIVE FORCE (emf) o cell voltage or cell potential (E) o Driving force that pushes the electrons to move from anode to cathode o Measure of the tendency of the cell reaction to occur ▪ Standard Electrode Potential, Eo ▪ Ionic Concentration = 1.0M ▪ Gases are at 1.0 atm pressure ▪ Temperature is 25°C or 298.15K ▪ Summarized in the standard reduction potential table standard reduction potential table ▪ Half-reactions are reduction half-reactions Strongest OA Weakest RA Weakest OA Strongest RA standard reduction potential table Zn is an anode (an electrode where oxidation occurs) reverse to make it reduction Zn Zn2+ + 2e- sign changes standard reduction potential table Cu is a cathode (an electrode where reduction occurs) already a reduction Cu + 2e 2+ - Cu sign is not changed 1. These are written as REDUCTION half reactions 2. Reversing the reaction: ▪ becomes OXIDATION half reaction ▪ the sign of the potential changes Example: Fe(s) → Fe2+(aq) + 2e- Eo = 0.44 v 3. Multiplying the reaction by a factor ▪ the value of the potential remains the same Example: Fe2+(aq) + 2e- → Fe(s) Eo = - 0.44 v 3Fe2+(aq) + 6e- → 3Fe(s) Eo = - 0.44 v  ▪ generate electricity from spontaneous reactions ANOLYTE CATHOLYTE electrolyte solution electrolyte solution where anode is where cathode is immersed immersed INTERNAL CIRCUIT: consists of electrolyte in the salt bridge to maintain electrical neutrality  ▪ generate electricity from spontaneous reactions ANIONS: must flow CATIONS: flow towards towards the anolyte to the catholyte to neutralize the charge of neutralize the anion cation that accumulates after oxidation ▪ generate electricity from spontaneous reactions Oxidation: Cu → Cu2+ + 2e- Eo = - 0.34 v Reduction: (Ag+ + e- → Ag) x 2 Eo = +0.80 v Overall: Cu + 2 Ag+ → 2 Ag + Cu2+ Eo = +0.46 v spontaneous reaction Multiply the reduction reaction by 2 to balance the number of electrons involved. Parameter Galvanic Cell Energy conversion Chemical energy to electrical energy Spontaneity of reaction Spontaneous E cell Positive Reaction at the anode Oxidation half reaction Reaction at the cathode Reduction half reaction Polarity of anode Negative Polarity of cathode Positive Electron flow Electron moves from anode to cathode Movement of anions Anions move towards the anode (anolyte) Movement of cations Cations move towards the cathode (catholyte)