# Homework Help: Ideal Gases

1. Jan 3, 2006

### chineseman1

I have been trying to do this questions for about 30 minutes right now and its a one dot questions. I think I am converting the atoms wrong. Could someone help me?

A typical region of interstellar space may contain 10^6 atoms per cubic meter (primarily hydrogen) at a temp of 100 K. What is the pressure of the gas?

>Okay, what I have done was use PV=nrT, but I am having trouble converting it. Do I take the atoms and divide by avogadros?

Thank You.

2. Jan 3, 2006

### Integral

Staff Emeritus
It depends on what value of r you are using. Your units need to match.

3. Jan 3, 2006

### chineseman1

I am using 8.31.

4. Jan 3, 2006

### LeonhardEuler

For future reference you should post homework problems in the homework section-where this thread will probably be moved to in a minute anyway.

Anyway, you have 106 atoms in 1 m3. 106 atoms is:
$$10^6 atoms\times\frac{1mol}{6.02\times 10^{23} atoms}\approx1.66mol$$
in one m3. Convert m3 to L by multiplying by 1,000 then you can use the ideal gas law.

5. Jan 3, 2006

### LeonhardEuler

Always keep in mid what units you are using. $R=8.31\frac{J}{K\cdot mol}$ so you better not convert to liters after all because $1J=1\frac{kg\cdot m^2}{s^2}$, so the unit of volume is the m3

6. Jan 3, 2006

### chineseman1

Okay. So I was doing it right!
But when I do use the Ideal Gas Law I get 1.37E-19, while the answer in my book is 10^-15. So I really don't know what I am doing wrong here. I as doing P= nRT/V, so I just plugged in all my variables and still not getting right answer.

7. Jan 3, 2006

### Bystander

Take another look at your bookkeeping on exponents.

And, review comments on significant figures.

8. Jan 3, 2006