Sulfate is reduced under anoxic conditions. Sulfate reduction is shown in follow

Question

Sulfate is reduced under anoxic conditions. Sulfate reduction is shown in following (unbalanced) equation: CHO + SO_4^2- + H^+ rightarrow CO_2 + HS^- + H_2O. a. What are the oxidation states of each element in the equation? Write the number under the element in the equation. b. Write the half reactions. c. Label which half reaction shows oxidation and reduction. d. Balance each half reaction. e. Write is the full balanced equation. f. What is the change in Gibbs free energy? g. What is the reduction potential? h. Will this reaction produce energy for bacterial growth?

Explanation / Answer

1. Oxidation state of each elements

C(+4)H(+1)O(-2) + S(+6)[O(-2)]-24+ H(+1)---------------->C(+4) O2(-2) +S(-2)H (+1) +H2(+1) O(-2)

2. Half reaction

SO42-+H+---------------->HS-  and CHO---------------->CO2

C. Reduction

SO42-+H+---------------->HS-

Oxodation

CHO---------------->CO2

d. Balance half cell

SO42- + 9H++ 8e- ---------------->HS-+ 4H2O-------------------------1

4CHO+ 3O2---------------->4CO2+2H2O + 8e-------------------------2

e. full balancd euation obtained by mixing eq 1 and 2

SO42- + 9H++4CHO+ 3O2 +8e- ----------------------->4CO2+2H2O +HS-+ 4H2O+ 8e-

common part get cancelled

SO42- + 9H++4CHO+ 3O2----------------------->4CO2+ HS-+ 6H2O

f. Gibbs free energy change is occure during the chemical reactions. The change in gibbs free energy is equal to the change in the enthalpy of the product minus the change in the reactantat constant temperature.

Gibbs free energy=deltaG(product)-delta G(reactant).

Reduction pottential- the ammmount of current reuired for the reduction of the specis called as reduction potential.

eg.

Ce4+ + e-1-------------------->Ce3+ reduction potential is 1.61 v

h.  H+ generate during reaction (glycolysis and the TCA cycle) to reduce some compound other than O2. This can produce energy for bacterial grouth.

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