LECTURE 6A

YOUTUBE

  • redox reactions - type of reactions involved in electrochemistry

review of redox reactions

slide 3

  • bumaba ang oxidation number kaya reduction

  • tumaas ang oxidation number kaya oxidation


    slide 4


  • left n right box - half cells

  • pink box salt bridge

  • violet wire where the elctrons can flow

slide 5

  • green box oxidation - the copper ions are present in the solution of cuso4, while the copper metal is present as the metal electrode aka anode

  • note: AN-OX

  • during redox reaction, copper metal is converted to copper ions resulting to THINNING of the anode due to the decreasing amount of copper metal as the reaction proceeds. this will also result to formation of electrons that will flow through the external circuit.

slide 6

  • yellow box reduction - the silver ions are present in the soln of silver nitrate while the silver metal is present as the metal electrode with is cathode

  • note: RED-CAT

  • during redox, silver ions are converted to silver metal resulting to THICKENING of the cathode due to the increasing amount of silver metal as the reaction proceeds

  • this will require absorption of electrons that are generated from the previous reactions

slide 7

  • pink box salt bridge - to keep the solution electrically neutral

  • ions present are potassium and chloride ions

  • the negatively-charged chloride ions are directed towards the oxidation half cell, this is to neutralize the charge of the anode which produces positively charged copper ions

  • the positively charged potassium ions are directed towards the reduction half cell, this is to neutralize negatively charged nitrate ions that are left alone by the silverr ions converted to silver metals

slide 8

  • violet box external circuit or wire - electrons are moving from the anode going to the cathode

  • electrons are produced during oxidation and these electrons will be consumed in the reduction half reaction

  • that is why the electrons are going from the anode to the cathode

slide 9

types of electrochemical cells

  • voltaic cell - energy is produced from a spontaneous redox reaction

  • electrolytic cell - energy is supplied to make a nonspontaneous redox reaction

  • deltaG represents the gibb’s free energy change of the reaction

  • NOTE: deltaG or free energy change tells us the spontaneity of the reaction

  • deltaG < 0 - sponti (salute)

  • deltaG > 0 - nonsponti (wink)

  • once equilibrium is reached, the cell potential will be equal to 0 volts

slide 10

cell notation

  • the two vertical lines corresponds to the phase boundary bet half cells

  • the oxidationhalf reation or the anode is shown on the left

  • the reduction half reaction or the cathode is shown on the right

  • reaction of zinc metal and copper ions - the left side of the notation corresponds to the oxidation hr which shows that zinc metals oxidizes to form zinc ions

  • the right side of the cell notation, the reduction of the copper ions to copper metals is shown

slide 11

  • kapag walang solid sa isang hr pwede maglagay ng inert metal as electrode

  • example: the reaction still corresponds to the zinc metals to zinc ion (same as before); right side corresponds to reduction of iron 3+ ions to iron 2+, here we can see that the inert electrode platinum is not part of the hr

slide 12

cell potential

  • E right - corresponds to the cell potential of the cathode or the reduction hr

  • E left - corresponds to the cell potential of the anode or the oxidation hr

  • reduction always on the right , oxidation always on the left

slide 13

  • the standard hydrogen electrode has been used as a universal reference electrode because it gives a standard electrode potential of 0 volt.

slide 14

  • deltag or free energy change of the system tells the spontaneity of the reaction

  • left side of the triangle

  • deltag naught can be solved if you have the calculated enaught cell or the standard cell pot

  • n - corresponds to the balanced number of electrons transferred in the redox

  • f - faraday;s constant (96,485 C/mol)

  • right side of the triangle

  • if the deltag is already calculated, it can be used to calculate the equi constant K

  • r- gas constant

  • t - temp of the system

  • since we are using naught , constant ang temp at 25 deg celcius

  • k value can be solved using the e naught cell value

  • NOTE: if you can solve for the e naught cell values, you can readily solve the delta g naught and k values

slide 15

SP1: solving k from e naught

  • givens and unknowns

  • e naught can be obtained from ref table

  • if you are given the reaction, make sure it is balanced and you know how to write in half reactions