Hi,(adsbygoogle = window.adsbygoogle || []).push({});

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.

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Please Help me with some Chemistry Questions

**Physics Forums | Science Articles, Homework Help, Discussion**