Concentration of nitrogen oxide in air

The mole fraction of NO can be calculated using the ideal gas law, and then the mole fraction of NO2 can be found using the equilibrium constant for the reaction. The sum of the two mole fractions should equal 5 ppm, allowing you to solve for the mole fraction of NO and convert it to parts per million.
  • #1
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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.
 

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  • #2
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.
 
  • #3
Pose this in the chemistry section of PF.
 
  • #4
Woopydalan said:

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.
 
  • #5
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
 

1. What is the concentration of nitrogen oxide in the air?

The concentration of nitrogen oxide in the air varies depending on location and time, but on average, it is around 0.3 parts per million (ppm) in urban areas and 0.05 ppm in rural areas.

2. How does the concentration of nitrogen oxide in the air affect human health?

Nitrogen oxide is a harmful pollutant that can cause respiratory problems, such as asthma and bronchitis, and can also contribute to the formation of smog and acid rain. Long-term exposure to high levels of nitrogen oxide can also increase the risk of heart disease and lung cancer.

3. What are the main sources of nitrogen oxide in the air?

The main sources of nitrogen oxide in the air are human activities, such as transportation (cars, trucks, planes), power plants, and industrial processes. Natural sources, such as lightning and wildfires, also contribute to the concentration of nitrogen oxide in the air.

4. How is the concentration of nitrogen oxide in the air measured?

The concentration of nitrogen oxide in the air is measured using specialized instruments, such as gas analyzers and spectrometers. These instruments can detect and quantify the amount of nitrogen oxide in the air samples collected from different locations.

5. What are the effects of reducing the concentration of nitrogen oxide in the air?

Reducing the concentration of nitrogen oxide in the air can have several positive effects, including improved air quality, reduced health risks, and decreased environmental damage. It can also help mitigate the effects of climate change by reducing the formation of greenhouse gases.

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