Please answer all questions fully! 1. Consider the reaction CH3CH2CH20H + H2CrO4

Question

Please answer all questions fully!

1. Consider the reaction CH3CH2CH20H + H2CrO4 - CH3CH2COOH [H2CrO3]. The uncatalyzed reaction has the following characteristics: - Reaches equilibrium in 60 minutes G0-12 kJ mol-1 The alcohol first forms an aldehyde transition state, which is then oxidized to the acid - .The complete reaction is not shown for simplicity (and is therefore not balanced) Based on this, answer the following questions about the reaction at 25°C: a) At equilibrium, will there be more Propanol or Propionic acid? Explain. b) Imagine you are designing an enzyme to carry out this reaction. What amino acids might you put in the active site of your enzyme? Why? c) If an enzyme catalyzes this reaction, predict the concentration of propionic acid at the end of the reaction, if I started with 1 mole each of propanol and chromic acid (at STP). How long would it take for the catalyzed reaction to be complete? Explain.

Explanation / Answer

(A) In a chemical reaction that can proceed in the forward or the reverse direction, equilibrium is the state in which both reactants and products are present in concentrations which have no further tendency to change with time. This state is usually obtained when the forward reaction proceeds at the same rate as the reverse reaction.

Therefore, if the given reaction is at equilibrium, then the amount of propanol and proionic acid will be the same.

(B) In the given chemical reaction propanol undergoes oxidation to form propionic acid. An enzyme that catalyses such a reaction is called as alcohol dehydrogenase. All alcohol dehydrogenases have a histidine and two cysteine residues in its active site along with a Zinc ion.

Hence to catalyse this reaction an enzyme with histidine and two cysteines in the active site must be designed.

(C)If an enzyme is used to catalyse this reaction, then the reaction is forced to proceed in only one direction.THerfore, the enzyme will allow the conversion of propanol to propionic acid but not the conversion of propionic acid to propanol. Hence, all of propanol will be converted propionic acid.

If at the begining of the reaction 1 mol of propanol is present, by the end of the rection all of it will be converted to propionic acid. Therefore 1mol of propionic acid will be obtained at the end of the reaction.

In an non-catalysed reaction, i.e. reaction where both forward reaction and reverse reaction take place, equilibirum is achieved after 60 min. This means that after 60 min equal amounts of propanol and propinoic acid are found. Therfore, for every molecule of propanol converted into propinoic acid, an equal amount of propinoic acid is converted bact to propanol.

If the same reaction is catalysed, only forward reaction takes place i.e. the conversion of propanol to propinoic acid. Therefore if a molecule of propanol is converted to propinoic acid, a molecule of propanol is not generated back from propanol. Hence the reaction will be completed within 60 min.

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