Consider the following half reaction in which nitrate is reduced to nitrite: no3– 2h 2e– → no2– h2o. the reaction has a δg°' value of –81 kj/mol. the negative value of δg°' results from the very e°' value of the redox couple no3–/no2–, and it reflects the strong tendency of nitrate to electrons. choose one: a. positive / donateb. negative/ acceptc. negative / donated. positive / accept

D. positive/accept

Explanation:

a) The standard gibbs free energy (ΔG⁰) is related to the standard cell potential (E⁰) as follows:

where n = number of electrons

F = faraday constant

The given half  reaction reaction has ΔG⁰ = -81 kJ/mol. Based on equation (1) a negative value for the free energy can be obtained only if E⁰ is positive.

Thus, the negative value of ΔG°' results from the very positive value of E⁰

b) The value of E⁰ is the standard reduction potential which reflects the tendency of the system to accept electrons and get reduced. Higher (more positive) the value, greater will be the tendency to accept electrons.

Therefore, the positive E⁰ value of the redox couple NO3–/NO2– reflects the strong tendency of nitrate to accept electrons.

"standard molar enthalpy:

h2o ( liquid water ) : - 285.8 kj/mole

h2o ( water vapor ) : - 241.8 kj / mole.

δhrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0

answer: 44.0 kj"