Question

The bacterium nitrobacter can oxidize nitrite to nitrate as a source of energy for growth. Write a balanced chemical reaction for the reaction of oxygen (g) with nitrite (aq) to form nitrate (aq). The heat of formation of nitrite (aq) is -104.6 kJ/mol. The free energy of formation for nitrate (aq) is -37.2 kJ/mol. The data for nitrate (aq) and O2 are in the back of your book. Use this information to determine the heat of reaction and the free energy of reaction for the conversion of nitrite to nitrate. Then determine K for this reaction and ∆S for this reaction. Finally determine the absolute entropy of nitrite (aq) based on this data.

delta G for O2 = 0

delta H for O2 = 0

delta G for NO3 = -108.74

delta H for NO3 = -205

Answer 1

The balanced reaction for formation of nitrate by nitrobacter is:

  .....................1

Now, the reactions for the formation of nitrite and nitrate respectively are:

....................2

....................3

Now, if we reverse the equilibrium-2 for nitrite, it becomes:

.....................4

Now, add the reactions 3 and 4 to get the reaction for the formation of nitrate by the nitrobacter.

Therefore, if we add the for the reactions 3 and 4 , to get the for the reaction-1.

But be careful that we have the for the formation of nitrite, but the equation-3 has been achieved by reversing the equation-2, therefore we have to take the values with the signs just reversed (i.e. negative to positive and vice versa).

Therefore, the for the reaction-1 is as follows:

Now, we know that

Therefore,

or, (answer)

We know,

Therefore,

or, (answer)

Now the absolute entropy of nitrite (aq) or the entropy of the formation reaction is:

or,   (answer)