Concentration of nitrogen oxide in air

[member 392791]

Homework Statement

The relative compositions of the pollutants NO and NO2 in air are governed by the reaction

NO + 1/2 O2 ⇔NO2

For air containing 21-mol% O2 at 25C and 1.0133 bar, what is the concentration of NO in parts per million if the total concentration of both nitrogen oxides is 5 ppm? Note ppm is taken on a molar basis for gases.

Homework Equations

The Attempt at a Solution

For this problem I am not sure how to go about it. I am not 100% sure if ppm means moles/total moles. Also, I am not able to find out the concentration of NO2 at equilibrium, which is why I haven't been able to get the concentration of NO.

 

[NascentOxygen]

My chem study is too long ago to be able to help you. But I think I'd be looking for some sort of equilibrium constant at that temp & pressure, to be able to relate the proportion of moles of NO2 to NO. Do you have that?

Have you tried a google search? Often you can find a worked example on which you can base your approach.

 

[rude man]

Pose this in the chemistry section of PF.

 

[Chestermiller]

Homework Statement

The relative compositions of the pollutants NO and NO2 in air are governed by the reaction

NO + 1/2 O2 ⇔NO2

For air containing 21-mol% O2 at 25C and 1.0133 bar, what is the concentration of NO in parts per million if the total concentration of both nitrogen oxides is 5 ppm? Note ppm is taken on a molar basis for gases.

Homework Equations

.

The Attempt at a Solution

For this problem I am not sure how to go about it. I am not 100% sure if ppm means moles/total moles. Also, I am not able to find out the concentration of NO2 at equilibrium, which is why I haven't been able to get the concentration of NO.

In this context, ppm means mole fraction times 1 million.

 

[rezeew]

Could you please provide a more detailed explanation of the problem and your thought process? Thank you.

I can provide a response to this problem by first clarifying the meaning of "ppm". In this context, ppm stands for "parts per million" and it is indeed taken on a molar basis for gases. This means that the concentration of a gas in ppm is equal to the number of moles of that gas divided by the total number of moles in the mixture, multiplied by 1 million.

Now, to solve this problem, we can use the ideal gas law to relate the concentrations of NO and NO2 at equilibrium to their partial pressures. Since the total concentration of both nitrogen oxides is given as 5 ppm, we can assume that the total pressure of the mixture is also 5 ppm. Therefore, the partial pressure of NO and NO2 must also be 5 ppm each.

Using the ideal gas law, we can write the following equations:

PNO = (XNO * Ptotal) / (XNO + XNO2)

PNO2 = (XNO2 * Ptotal) / (XNO + XNO2)

Where PNO and PNO2 are the partial pressures of NO and NO2, respectively, XNO and XNO2 are their mole fractions, and Ptotal is the total pressure of the mixture.

Since we are given that the mixture contains 21-mol% O2, we can calculate the mole fraction of O2 as:

XO2 = (21 mol/100 mol) = 0.21

Since the total pressure is given as 1.0133 bar, we can calculate the partial pressure of O2 as:

PO2 = (0.21 * 1.0133 bar) = 0.2126 bar

Now, using the equilibrium constant for the reaction, Kp, which is equal to PNO2 / (PNO * PO2^(1/2)), we can solve for the mole fraction of NO, XNO:

Kp = PNO2 / (PNO * PO2^(1/2))

5 ppm / (XNO * 0.2126 bar^(1/2)) = 1.2 * 10^-4 (at 25C)

Solving for XNO, we get:

XNO = 0.00103

Therefore, the concentration of NO in parts per million