The Pressure in Interstellar Space.

[TOMMiB]

Homework Statement

Interstellar gas consists of a mixture of H and He molecules (10^4) and (10^3) respectively (in a 1m^3 volume). What is the pressure of the gas if the temperature is 80K?

Relevant Equations

PV = nRT

n = 11000 because n = N/V and V = 1m^3.

Using P = nRT/V I get that P = 7.32x10^6 Pa.

considering that the gas is in a high vacuum, this value seems far too high to be true.
Please help?

 

[PeroK]

Homework Statement: Interstellar gas consists of a mixture of H and He molecules (10^4) and (10^3) respectively (in a 1m^3 volume). What is the pressure of the gas if the temperature is 80K?
Homework Equations: PV = nRT

n = 11000 because n = N/V and V = 1m^3.

Using P = nRT/V I get that P = 7.32x10^6 Pa.

considering that the gas is in a high vacuum, this value seems far too high to be true.
Please help?

What unit are you using for $n$?

 

[TOMMiB]

What unit are you using for $n$?

I have no unit, as it is simply the number of molecules in the system, I think.

 

[PeroK]

I have no unit, as it is simply the number of molecules in the system, I think.

You could always double check.

 

[Orodruin]

I have no unit, as it is simply the number of molecules in the system, I think.

Recheck the ideal gas law. What are the different variables it contains and their units?

(Also check that you end up with atmospheric pressure for conditions relevant at the Earth’s surface.)

 

[robot6]

Yes, most importantly here is to check the units that you are using for R. If you use $8.314 m^3 Pa K^{-1} mol^{-1}$, for example, then n should be in moles... A good source for various values of R is here:

https://en.wikipedia.org/wiki/Gas_constant