Transcribed By Angela Vivien Dela Cruz Lorraine Claire Lanuza Topics Electrochemistry Nuclear Chemistry ELECTROCHEMISTRY Processes that involves oxidation reduction reactions Energy is released by a spontaneous Electrical energy is used to cause a reaction and is converted to electricity nonspontaneous reaction to occur Oxidation half reaction loses electrons Reduction half reaction gains electrons OXIDATION NUMBERS 1 2 free elements uncombined states have and oxidation number of ZERO Na Be K Pb H2 O2 P4 In monatomic ions the oxidation number is equal to the charge of the ion Li Li 1 Fe3 Fe 3 O2 O 2 3 The oxidation number of oxygen is usually 2 in H2O and O22 it is 1 4 The oxidation number of hydrogen is 1 except it is bonded to metals in binary compounds in these cases its oxidation number is 1 5 Group 1A metals are 1 Group IIA metals are 2 6 and fluorine is always 1 the sum of the oxidation number or ion is equal to the charge on the molecule or ion BALANCING REDOX REACTIONS 1 write the unbalanced equation for the reaction in ionic form 2 separate the equation into 2 half reactions oxidation Reduction 3 Balance the atoms other than Oxygen and Hydrogen in each half reaction for reactions in acid add HCO to balance O atoms and H to balance H atoms 5 add electrons to one side of each half reaction to balance the charges on the half reaction if necessary equalize the number of electrons in the 2 half reactions by multiplying the half reactions by appropriate coefficients 4 6 Course Professor s Mr Luisito Salting 7 add 2 reactions together and balance the final equation by inspection the number of electrons on both sided must cancel GALVANIC CELLS Electrochemical cells where the reaction proceeds Involves a cell diagram anode salt bridge and simultaneously cathode A Zn rod is placed into a ZnSO4 solution at the anode and a Cu rod is placed into a CuSO4 solution at the cathode A KCl salt bridge is placed between the cells allowing for ions to pass through the bridge between the anode and cathode At the anode Zn atoms are oxidized to produce zinc ions and two electrons Zn s Zn2 aq 2e The electrons are passed externally to the cathode creating a current that lights a bulb When the electrons reach the cathode copper II ions are reduced to form Cu atoms 2e Cu2 aq Cu s Balancing the reaction Anode Zn s Zn2 aq 2e DELA CRUZ LANUZA BATCH 2024 Page 1 of 10 Transcribed By Angela Vivien Dela Cruz Lorraine Claire Lanuza Topics Electrochemistry Nuclear Chemistry Cathode 2e Cu2 aq Cu s E 0 SHE Example Course Professor s Mr Luisito Salting Net reaction Remember Zn s Cu2 aq Zn2 aq Cu s Reduction Cathode RedCa Oxidation Anode OxAn The difference in electrical potential between the anode and cathode is called Cell voltage Electromotive force emf Cell potential Cell Diagram Phase Boundary the transformation or differentiation of phases Instead of arrow single vertical line is used to show Ex solid aqueous or 1 atm in gaseous phase Concentrations outside standard conditions 1 M one molar concentration in standard condition may vary STANDARD REDUCTION POTENTIAL E reaction compound measurement of voltage associated with a reduction it measures the ability of a compound to oxidize other stoichiometry constants does not change the value of E only reversal of the reaction can change the sign of E the more positive E the greater the tendency to be aqueous solutes are at 1M concentration gases are at 1 atm pressure reduced E 0 oxidizing agent E 0 reducing agent DELA CRUZ LANUZA BATCH 2024 E A 0 7 V reducing E B 0 5 oxidizing note E A is higher value so it is most likely to be reduced C will be the product of A because it would be D will be the product of B because it would be reduced oxidized STANDARD HYDROGEN ELECTRODE SHE E 0V STANDARD EMF E cell E cell E cathode E anode E cell E right E left SPONTANEITY OF REDOX REACTIONS G nFEcell n number of moles of electrons in the reaction G nFE cell 96 500 96 500 G RTlnK nFE cell presence of knot reaction Page 2 of 10 Transcribed By Angela Vivien Dela Cruz Lorraine Claire Lanuza Topics Electrochemistry Nuclear Chemistry Equations to use E cell 0 0257 E cell 0 0592 or Relationships Among G K and E cell G RTlnK nFE cell G K E cell Reaction Under Standard State Conditions neg 0 1 1 pos Favors formations of products 0 Reactants and products are in equilibrium equally favored pos 1 neg Favors formation of reactants EFFECT OF CONCENTRATION ON CELL EMF Nernst Equation Determining cell potential outside standard conditions at 298K Equations to use 0 0257 0 0592 CONCENTRATION CELLS Galvanic cell from two half cells composed of the same material but differing in ion concentrations ELECTROLYSIS Electrical energy to cause a non Galvanic cell spontaneous Electrolysis non spontaneous chemical reaction to occur is used spontaneous DELA CRUZ LANUZA BATCH 2024 Course Professor s Mr Luisito Salting Electrolysis of molten NaCl anodes are used NaCl melts at 801 C so iron cathodes and carbon At the cathode liquid sodium atoms are formed Liquid sodium is less dense than molten NaCl so the liquid Na rises to the top and can be transported out of the cell At the anode chlorine gas is formed which can bubble Because the electrolysis of NaCl is nonspontaneous a Electrons flow from the anode where Cl2 gas is produced from chloride ions through the battery to the cathode which forms liquid sodium atoms from sodium atoms battery is needed to drive the reaction up and be transported out of the cell Electrolysis of Water Two nonreactive metals serve as electrodes and are At the anode water is oxidized to produce O2 gas submerged in a dilute H2SO4 solution protons and electrons Page 3 of 10 Transcribed By Angela Vivien Dela Cruz Lorraine Claire Lanuza Topics Electrochemistry Nuclear Chemistry The electrons are then circuited through the battery to the cathode where the reduction of protons causes formation of H2 gas Course Professor s Mr Luisito Salting In an electrolysis set up the volume of H2 produced is twice that of O2 because twice as much H2 gas is generated Volume oxygen hydrogens ELECTROLYSIS AND MASS CHANGES Charge C current A x time s 1 mol e 96 500 C By measuring the current in amperes and time in seconds the charge in coulombs can be calculated By dividing the charge by the Faraday constant the Using the mole ratio of the half cell reaction the moles Using the molar mass or the ideal gas equation the number of moles of electrons can be calculated of substance oxidized or reduced can