[Pliz89]

Hello,

I got this assignment.

Normal air (0.78% N2, 0.21% O2) is held at 2000K long enough to reach chemical
equilibrium with NO and NO2. Assume that the only reactions involving NO and NO2 are:
1) N2 + O2  2NO
2) NO + 0.5O2    NO2

The equilibrium constants obtained at 300K for the formation of NO and NO2 are:

for 1) Keq:7 x 10^-31
for 2) Keq: 1.4 x 10^6

The standard heats of formation at 25ºC are:
HfºN2 = 0, HfºO2 = 0, HfºNO = 90.25 kJ/mol, HfºNO2 =33.2 kJ/mol

Please, could you help me about:

point.a) Using Van’t Hoff equation, Calculate the concentrations of all components when equilibrium is reached at 2000K

point.b) Plot the calculated equilibrium concentration of NO at two different oxygen contents of the reacting gas. Case 1 :78% nitrogen, 21% oxygen; and case 2: 78% nitrogen, 4% oxygen in a temperature range between 300 and 4000K

Thank you

[Borek]

Please read the forum rules.

[Pliz89]

I tried to find Delta H initial reaction and Delta G initial reaction. At equilibriul Delta G final is equal to = 0 so I can find K constant. Using the 0.78 N2 and 0.21 O2 as initial concentration I can Find all concentration for the first reaction.

I tried to do the same for the second reaction but I don't know the initial concentration of NO so I have not idea how can go to the next step.

About point b. I tried to get the concentration at equilibrium of NO calculating "x" at 300K trough Keq (from point a) = [Concentration NO]^2/ conc [NO]* conc [O2].
I calculated Keq at 4000K by van't hoff equation (Delta T= 1/4000 - 1/300) and in the same way to above I found "x" (and then the concentration of NO at equilibrion for 2 different temperature.
I plot that in a graph temperature versus concentration but I got just to point in 2 different temperature. I'm not sure it is correct.

[Babcock_Hall]

You wrote, "At equilibriul Delta G final is equal to = 0 so I can find K constant."  I am not completely sure where your problem lies, but there is a difference between ΔG and ΔG°.  ΔG = 0 at chemical equilibrium; ΔG° is related to the equilibrium constant.  I do not know what you mean by ΔG initial reaction.

[Pliz89]

yes right. This is my point. I talked about Delta G at chemical equilibrium