How Changes to Half Cell Affect Ecell

Let's consider the following electrochemical cell: Pt(s) | Fe2+(aq) , Fe3+(aq) || Ag+(aq) | Ag(s) Fe2+ is oxidised to Fe3+ hence the iron half cell is the anode. Ag+ is reduced to Ag so the silver half cell is the cathode. We want to predict what happens to cell potential (Ecell) when changes are made to a half cell. When the change shifts the position of equilibrium (POE) for the reversible electrode, E value will be affected since electrode potential measures the tendency for forward reaction (reduction). When POE shifts right, forward reaction is favoured hence E value increases. When POE shifts left, forward reaction is disfavoured hence E value decreases. Remember to use the reduction half equation when considering shifts in POE as E values are based on reduction half equations in the Data Booklet. Let's consider the following 3 changes: 1. Solid NaCl added to silver half cell When NaCl is added, silver cations will be precipitated as AgCl(s). Concentration of Ag+ will decrease and POE for Ag+ + e- = Ag will shift left. Forward reaction is disfavoured hence E value for Ag half cell will decrease. Since Ag half cell is the cathode, a decrease in Ereduction will cause Ecell to decrease. 2. Dipping the silver electrode deeper into the solution Changing the surface area or shape of electrode in contact with the solution has no effect on E value. Hence there will not be any changes to Ecell. 3. Solid FeCl2 added to iron half cell When FeCl2 is added, concentration of Fe2+ increases. POE for Fe3+ + e- = Fe2+ will shift left, forward reaction disfavoured and E value for Fe half cell will decrease. Since Fe half cell is the anode, a decrease in Eoxidation will cause Ecell to increase. Topic: Electrochemistry, Physical Chemistry, A Level Chemistry, Singapore Please SUBSCRIBE to my channel and SHARE this video with your friends if you find it helpful! View the full video with description at my website https://chemistryguru.com.sg/how-changes-to-half-cell-affect-ecell This video is extracted from our Chemistry Guru on-demand video lessons. Learn A Level Chemistry online anytime, anywhere and at your own pace! Find out more at https://chemistryguru.com.sg/on-demand-video-lesson