# Homework Help: Calculate CO concentration at high altitude

1. Jun 12, 2014

### jwingeart

Question:
You are cooking in a tent at 17,000ft with outside air temp at -15F. The concentration of CO in the tent is 40ppm. Calculate the equivalent CO concentration in mg/m^3.

First, I converted 17000ft to atm and got 501.5atm, which seems very wrong.

Next, I converted -15F to 247.039K.

I applied the Ideal Gas Law, PV=nRT

I tried to solve for V.

p=501.5 atm
n(molecular weight CO)=28
R (should be a constant)=.082056
T=247.039

I come up with a ridiculous answer. It seems simple, but I can't figure out where I'm going wrong.

2. Jun 12, 2014

### jwingeart

Forgot to mention also, (but it's obvious) that the conditions are not at STP. (not 25C, not 1.0 atm)

3. Jun 12, 2014

### Staff: Mentor

Show us how you calculated the pressure at that altitude?

Chet

4. Jun 12, 2014

### SteamKing

Staff Emeritus
Why do you think altitude is equivalent to atmospheres? Your calculation assumes that there is a water column 17000 feet tall somewhere.

FWIW, this calculation is OK.

Well, for one thing thinking that the atmospheric pressure at 17000 feet altitude is 500 atmospheres. (Hint: the atmospheric pressure decreases with altitude, although not in a linear relationship.)

5. Jun 13, 2014

### SCP

Check your units. At 17,000 ft, atmospheric pressure should be ~500 kPa, or 0.5 atm. If the answer you're getting is off by 3 orders of magnitude, this might be why.

6. Jun 13, 2014

### D H

Staff Emeritus
So why didn't you stop right there?

It obviously is very wrong. When you get an answer that seems very wrong, you should stop and double check. Carrying a bad calculation forward is generally a very bad idea because that bad calculation oftentimes poisons all subsequent results.

That's wrong, too. One atmosphere is on the order of 100 kPa, so 500 kPa is about 5 atmospheres.

7. Jun 13, 2014

### SteamKing

Staff Emeritus
It's that damn metric system confusin' everyone again.

8. Jun 16, 2014

### SCP

Ah yes. I was thinking in millibars. Silly. In any case, at 17,000 ft you should get pressure at ~0.5 atm (or ~50 kPa).