Question

QUESTION 58 - WRITE YOUR ANSWER IN THE SPACE PROVIDED [5 marks Dichromate, Cr207 in acidic solution requires 6e to produce Cr(aq) and water. The electrons can come from the oxidation of Fe (aq) to Fe + (aq). a. Write balanced half reactions for these two reactions. [3 marks] b. Combine them to obtain an overall balanced equation for reduction of dichromate by Fe(aq). [2 marks] QUESTION 59-WRITE YOUR ANSWER IN THE SPACE PROVIDED 1 5 marks The activation energy for the decomposition of HI is 183 kJ/mol. At 573 K, the rate constant was measured to be 2.91 x 10 Ms. The frequency factor "A" is 1.40 x 10" Ms a. At what temperature in Kelvin does the reaction have a rate constant of 0.160 M s'?

Answer 1

balancing Ion-Electron method for ancing redox half-reaction Step: -1 To find redon and separate reactions. half reactions the two half-cele oxidation half cell: Reduction halfcens Felt fe3t crgot a Step 2 cost Assign each the oxidation number on atoms both sides. oxidation halfwei Reduction half-celli Fe 3+ Step: 3 er not To balance 34 atoms other than it oxidation half ceni Redue ton half cella felt Fe 3+ Cr207 step: oxygen an Balance on and hydrogen atoms @ Balance the ony jen atoms with H₂O. • Balance the hydrogen atoms with Itt In a basic medium, add one oH each side for every Ht onida tahon half-cen: Redue ton half-cen: half-cen: Step-r crgo7 +14H 23+ Balancing charge a for an daction , add e are a for reduction, add es side + 7 H₂O product side on react

aridation half-cle: Fe2+ Reduction half-cell: Fe3+ +le- C,07 + 4H+ + Ce Step-si 20x5t + Balancing H2O elee trons onidation half-cen: Fe 2+ Reduction half-cell: 6 Felt fe3+ + le-] 16 →6 Festaben Step-t: (r207 +14H+ + 6e Add the two 6 fe 2+ half-cen 2 Cr3+ + 7H2O reactions, + Cr₂07 +14H+ +6é step.8: ote? Now the balaned reaction is, +2erst + 7H2o f 66n. chemical reduetion FeaTCV07 + Auf 0759 6 Fe e 57 + 20457 +2 CT According + 7+20 Arrhening equation, Ea- Activate an Taking logarithan, loge = logA - K = Rate constant As frequency Suppose factor at two differenr tempera say. 'T' and 'T the ki, ka then, rate constants are long enou) - 5039(+-+) ftest

Given that, Acteration energy Ea) = 183 k5hmal at and Ti=5734 (183 x1000) Fork k, = 2.91x106 mis Kp = 0.160 m/s. Iz 2? Re 8314 g/molike According to Arrhenius equation, log C) - pagoga ( t ) a log cover that too) - 9233 ziy (Gent) 4.74 = 9557.56 (174527103 - ) 0.160 2-91x106 ñ ñ 183 x loro 2.303 *8.314 4:9594810 4 = 1.7452x10 3 - 1 / ñ - 1.2492*10-3 Tz a 800.512 The required temperature will be- 800:5124