Can anyone please explain how i would balance this equation? This is most important, but i would also like to know how to find the equilibrium constant K at 298 degrees kelvin.

**Answer 1**

Write the oxidation and reduction in separate half reactions:

Oxidation:

Cu+(aq) —-> Cu2+(aq) + e-

Reduction:

4H+(aq) + NO3-(aq) + 3e- —-> NO(g) + 2H2O(l)

Since we’re in acidic solution, we can get rid of extra oxygen with H+, and gain needed oxygen by taking it from water. The reduction equation is ambiguous because you can form several nitrogen oxides as products, but I was able to find this one in the reduction potential table below.

Since each electron added to nitrogen in the reduction must come from copper during the oxidation, we must make the number of electrons in both half reactions the same. In this case, multiply the oxidation equation by 3 to get the number of electrons to be the same. Add 3*oxidation to the reduction equation – the electrons cancel and you get the net reaction:

Cu+(aq) + NO3-(aq) + 4H+(aq) —-> Cu2+(aq) + NO(g) + 2H2O(l)

The equilibrium constant can be found from the change in Gibbs free energy of the reaction.

At equilibrium,

ΔG° = -RTln(K), where K is the equilibrium constant, R is the gas constant, and T is temperature

This free energy change can be calculated from enthalpy and entropy values from a table, but it’s often difficult to find values for species in solution. A better method (and also the easiest one to do experimentally) is to calculate the electrochemical potential of the reaction and use the Nernst equation to get K. This potential can be calculated from the standard reduction potentials in a table like that linked below.

The Nernst equation:

ln(K) = nFE°/RT

where K is the equilibrium constant, n is the number of moles of electrons transferred in the reaction (3 in this case), F is Faraday’s constant, E° is the standard potential for the reaction, R is the gas constant, and T is temperature

Source(s): Balancing redox reactions:

http://chemistry.about.com/od/generalchemistry/ss/…

Equilibrium constant and free energy:

http://en.wikipedia.org/wiki/Chemical_equilibrium#…

http://en.wikipedia.org/wiki/Gibbs_Free_Energy#Use…

Reduction potentials:

http://www.jesuitnola.org/upload/clark/refs/red_po…

Nernst equation:

http://en.wikipedia.org/wiki/Nernst_equation#Relat…

**Answer 2**

Copper Oxidized

**Answer 3**

If you’re doing Mastering and looking for the balanced equation

3Cu+(aq)+4H+(aq)+NO3−(aq)→3Cu2+(aq)+NO(g)+2H2O(l)