Some reactions are inhibited by the prescence of another chemical. Oxidation rea

Question

Some reactions are inhibited by the prescence of another chemical. Oxidation reactions for instance are often inhibited by the presence of citric acid, hence why it is in ingredient in many packaged foods. It increases the shelf life significantly.

If you carried out a one trial of an oxidation reaction in which citric acid was present and one without it was present:

i) Could you determine the effect, if any, that citric acid has on the activation energy of the oxidation reaction?

ii) What additional information, if any, would you require to make the determination in the above question?

iii) Would you expect the acviation energy of the oxidation reaction be higher, lower, or the same with citric acid present? Please explain

Explanation / Answer

i)

To determine the effect, that citric acid has on the activation energy of the oxidation reaction we have to device an experiment. We will be calculating the rate of oxidation reaction with and without citric acid.

Rate law will be determined by

A + B ---> P

Rate = k[A^n][B^m]

Which k will then be used to calculate Energy of Activation, Ea by using formula,

k = Ae^(-Ea/RT)

where k is the rate constant, A is called the Arrhenius pre-exponential constant, Ea is the activation energy, R is the gas constant, and T is the temperature (in kelvin).

ii)

We will require molarities of solution and amount of Fe ions or another metal ion which catalyze oxidation reactions.

We can also additionally perform ion mass spectroscopy to get oxygen concentration on surface.

iii)

The mechanism of citric acid to prevent oxidation is by chelating metal atoms/ions which catalyze the oxidation reaction. Metal ions which are catalyst lower the activation energy for oxidation reaction. If we chelate those then indirectly activation energy will increase. But as if was before decreased bymetal ions, it will be unchanged if metal ions are chelated.

Activation energy remains unchanged.

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