A solution contains Fe²⁺, Fe³⁺ and I^$$-$$ ions. This solution was treated with iodine at 35^oC. E^o for Fe³⁺/Fe²⁺ is + 0.77 V and E^o for I₂/2I^$$-$$ = 0.536 V.
The favourable redox reaction is

The rate of the reaction :   2N₂O₅ $$ \to $$ 4NO₂ + O₂
can be written in three ways.

$${{ - d\left[ {{N_2}{O_5}} \right]} \over {dt}} = k\left[ {{N_2}{O_5}} \right]$$

$${{d\left[ {N{O_2}} \right]} \over {dt}} = k'\left[ {{N_2}{O_5}} \right];\,\,$$ $${{d\left[ {{O_2}} \right]} \over {dt}} = k''\left[ {{N_2}{O_5}} \right]$$

The relationship between k and k' and between k and k'' are

The half-life of a substance in a certain enzyme-catalysed reaction is 138 s. The time required for the concentration of the substance to fall from 1.28 mg L^$$-$$1 to 0.04 mg L^$$-$$1 is

The unit of rate constant for a zero order reaction is