If I inject 1 g of a gas in a closed volume, why should I expect different ppm(v) at different temperatures?
Shall it be the same ppm(v) regardless of the temperature since I am injecting the same amount of gas in the same closed volume? I think it will be different from the equation of state but I do not understand why. Please help. Any references?

Thank you,

Does the gas dissociate above some temperature in the range considered?

Edited September 23, 20196 yr by studiot

No it does not dissociate. What happens is, I place aluminum phosphide tablet in a closed volume and this tablet produces 1 g of phosphine when reacts with the H2O in the air. The H2O is more than enough in this closer volume. But from the experiment, I get different concentration (ppmv) at different temperatures. What I don’t understand is, why different ppm at different temperatures while we have the same 1 g of phosphine within the same volume. I think it has to be the same ppm?

the range of temperature is 15-35 C. 

That's a much better description of what you are doing.
Is this for gas chromatography or how are you measuring the phosphine concentration?

I don't have any experience of phosphine chemistry but

Lee has

Quote

Phosphine often contains some diphosphine.

 

Latimer and Hildebrand say

Quote

Phosphine decomposes readily upon heating

Though no details are given.

 

Perhaps someone with more knowledge will add to this??

This experiment is held in a fully sealed barrel and the phosphine concentration is measured by a wireless sensors placed in the middle. This paper https://academic.oup.com/jee/article-abstract/22/2/381/930456 is saying the weight/volume changes with temperatures according to the equation of state. Here I manipulated the equation of state to convert from g/m3 to ppm(v) at different T and P, image attached. But my big problem is, since the AlP always produces the same amount of phosphine (1 g) in the same volume, does this mean I should expect the same ppm(v) regardless of the temperature or there is something I am missing here. Because from the experiment I get different ppm(v) but this could be because of some sort of leakage or because the pressure increases but I do not know how to calculate for this pressure increase. 

Thank you for your help.

 

On 9/23/2019 at 3:55 PM, dino2 said:

If I inject 1 g of a gas in a closed volume, why should I expect different ppm(v) at different temperatures?

That is not the experiment.  The experiment is designed to determine the amount of the chemical that will be in the saturated vapor phase at different temperatures and pressures.  Along the lines of absolute humidity for 100% relative humidity at different temperatures and pressures.