2. Solving a chemistry problem

20. For redox element type: Pt | A, B || C, D | Pt according to the standard electrode potentials of half-elements (Quick reference book of physical and chemical quantities. Edited by K.P. Mishchenko, A.A. Ravdel. 1974) write an equation and calculate the equilibrium constant of the oxidation - reduction reaction. Calculate emf. element (T=298 K). Indicate whether it is possible to practically change the direction of the reaction by changing the concentration of the components Accept aH2O = 1 an = 0.2
N option A B C D aA aB aC aD
20 Ce4 Ce3 Co3 Co2 0.08 0.007 0.02 0.005
(H and H2O are involved in the reaction)