How Do Atmospheric Conditions at the Stratopause Compare to Sea Level?

[MooShoo]

Hi,

I am studying for a midterm and I need help on 2 practice questions from the textbook which I have no idea how to start.

The first one is:
Calculate the atmospheric pressure at the stratopause. What are the concentrations (mol m-3) of dioxygen and dinitrogen at this altitude? How do these concentrations compare with the corresponding values at sea level?

I have no idea how I am able to start this question. Any tips would be greatly appreciated.

The second one is:
At a particular temperature, the Arrhenius parameters for the reaction:

•OH + H2 → H2O + •H

Are A = 8 x 10^10 s -1, and Ea = 42 kJ mol-1. Given that the concentration of hydroxyl in the atmosphere is 7 x 10^5 molecules cm-3 and that of H2 is 530 ppbv, calculate the rate of reaction (units of molecule cm-3 s-1) for this process.

I have tried this question with other formulas but it just always ends up with a very very large number. Any tips would be greatly appreciated.

Thank You.

 

[GCT]

Hi, you need to show your approach to this question first, it's the policy here at PF.

 

[Blueshift5]

Hello,

I am happy to assist you with your chemistry questions. Let's start with the first one about atmospheric pressure at the stratopause. To begin, we need to understand that the stratopause is the boundary between the stratosphere and the mesosphere, located at an altitude of approximately 50 km above sea level.

To calculate the atmospheric pressure at this altitude, we can use the barometric formula which relates pressure, altitude, and temperature. We also need to know the atmospheric conditions at sea level, which are typically a pressure of 101.3 kPa and a temperature of 15°C.

Using the barometric formula, we can calculate the pressure at the stratopause by plugging in the values for altitude and temperature. This will give us the pressure in kilopascals (kPa). To convert this to atmospheres, we can divide by 101.3 kPa.

To determine the concentrations of dioxygen and dinitrogen at the stratopause, we can use the ideal gas law, which states that the number of moles of a gas is directly proportional to its pressure and inversely proportional to its temperature. We can use the pressure calculated earlier and the temperature at the stratopause (around -80°C) to calculate the number of moles of each gas. Then, we can convert this to molarity (mol m-3) by dividing by the volume of the atmosphere at the stratopause.

To compare these concentrations with those at sea level, we can use the same calculations with the pressure and temperature at sea level. Keep in mind that the concentration of gases in the atmosphere can vary depending on location, but this should give you a general idea of the difference between the two altitudes.

Moving on to the second question about the Arrhenius parameters for a reaction involving •OH and H2, we can use the Arrhenius equation to calculate the rate of reaction. This equation relates the rate constant (k) to the Arrhenius parameters (A and Ea), the temperature (T), and the gas concentrations.

To solve for the rate of reaction, we need to plug in the given values for A, Ea, and the concentrations of •OH and H2. Remember to convert the units of concentration to match the units given for the rate of reaction (molecule cm-3 s-1).

If you are getting a very large number for the rate of reaction, it