Most organic matter decomposition in ocean water and sediments is mediated by bacteria. Different species of bacteria are capable of utilizing different oxidants during organic matter oxidation. For example, aerobic bacteria oxidize organic matter with molecular oxygen. Denitrifying and sulfate reducing bacteria oxidize organic matter with nitrate and sulfate, respectively. a. Using acetate (CH

3

COOH) as a model organic compound, calculate standard free energies of reaction (ΔG

∘

) for organic matter oxidation via O

2

Assume that reactions occur in aqueous solution at 25

∘

C and 1 atm pressure. Use the ΔGG

∘

values given here: G

O

0

acetate =−396.6 kJ mol

−1

G

O

OO

2

(aq)=16.32 kJ mol

−1

Gaf

o

CO

2

(ag)=−386.23 kJ mol

−1

G

o

o

H

2

O=−237.18 kJ mol

−1

Simplified reaction stoichiometries are given below: CH

3

COOH

1

+2O

2

(aq)=2CO

2

(aq)+2H

2

O(l) 5. Does the reaction in question 4 occur spontaneously or not? How do you know?

The reaction in question 4 involves the oxidation of acetate (CH3COOH) by molecular oxygen (O2) to form carbon dioxide (CO2) and water (H2O). The standard free energy of reaction (ΔG°) for this reaction can be calculated using the standard Gibbs free energy of formation (ΔG°f) of acetate and the standard Gibbs free energy of formation (ΔG°f) of CO2 and H2O.

The standard Gibbs free energy of formation (ΔG°f) for acetate is given as:

ΔG°f(acetate) = -396.6 kJ/mol

The standard Gibbs free energy of formation (ΔG°f) for CO2 is given as:

ΔG°f(CO2) = -386.23 kJ/mol

The standard Gibbs free energy of formation (ΔG°f) for H2O is given as:

ΔG°f(H2O) = -237.18 kJ/mol

The overall reaction for the oxidation of acetate to form CO2 and H2O is given by:

CH3COOH + O2 → CO2 + H2O

Using the standard Gibbs free energy of formation, we can calculate the standard free energy of reaction (ΔG°) for the reaction as follows:

ΔG° = ΔG°f(acetate) + ΔG°f(CO2) + ΔG°f(H2O) - RT ln Q

where R is the gas constant, T is the temperature in Kelvin, and Q is the reaction quotient (Q = [products]/[reactants]).

Substituting the standard Gibbs free energy of formation values into the equation, we get:

ΔG° = (-396.6 kJ/mol) + (-386.23 kJ/mol) + (-237.18 kJ/mol) - (8.314 J/mol·K) ln ([CO2] / [CH3COOH])

Simplifying the equation, we get:

ΔG° = -1441.5 kJ/mol

Since the standard free energy of reaction is negative, the reaction is spontaneous and will occur in the forward direction at standard conditions. Therefore, The reaction in question 4 occurs spontaneously.

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