Chemistry Forums for Students > Undergraduate General Chemistry Forum
confused on the unit and need atm
sickness:
given CO2 of 4200ppm or 4200mg/L
Atomic mass of about 44g for CO2
making 4200 mg/L to 9.5*10^-2 mol/L
using P=(nRT/L) I get
9.5*10^-2*R*293.15 = 236.6
Question is what is the unit that I get on the 236.6 and if it is not atm is there a simple conversion for getting to atm
jdurg:
Okay, right here you're using the ideal gas law which is PV=nRT. They have given you the CO2 value as 4200 mg/L. So in one Liter you have 0.095 moles which you have correctly figured out. So right now everything is good. For your pressure, you can rearrange the ideal gas law to P=RT(n/L) which you have already done. So your calculations are fine. What you don't have right there is R. R is a constant value that does not change. It is something that you have to look up. When you look up the value of R, you will find it as R=SomeNumber (Pressure Unit*VolumeUnit)/(TemperatureUnit*mole). So if you want your units to be in atmospheres, you need to find the value of R which is for use with atmospheres. ;D
sickness:
the R constant I get is 8.314 J/mol*Kg
Does this work? This is what I used for the calculation
Is there another R value that gives me atm?
jdurg:
You are using the thermodynamic version of R. You need to find the one that is used in the ideal gas law. ;D
sickness:
This 8.314472 is what I get as the R in PV = nRT from my geochemistry book and many sources online so if you know something I do not and know a better number to use this would be most appreciated.
If there is not another number I have tried canceling the units and simplifying them and I am confused as to what it is. My partner on this project is convinced that it is giving us pascals and if I just knew for sure the unit I am sure I could get the proper conversion.
Again thx
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