Phil,
That's the way I was leaning (zero order). Although I am not sure I am comfortable with your reason.  Temperature and pressure are indeed remaining constant as I do this in each run.  The reason I ask is that someone else (not on TechNet) called this first order.  So I took my results and plotted concentration vs. time and got a straight line (implies zero order) and then plotted ln[a0/(a0-x)] as a function of time and got a line that is ALMOST straight. R2 =  for drawing as zero order is always greater than drawing for first order, but not by much - 0.964 vs. 0.962, 0.9996 vs. 0.9995, 0.9994 vs. 0.935, etc.
Bev

-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: December 17, 2003 2:52 PM
To: [log in to unmask]; Bev Christian
Subject: RE: [TN] Need a chemist or chemical engineer to answer


hi,

i don't see this as a chemical reaction.  i see it as a physical change in state.  assuming temperature and pressure remain constant, the rate of change of solid into gas would remain constant and thus a '0' order operation.

phil

-----Original Message-----
From: Bev Christian [mailto:[log in to unmask]]
Sent: Wednesday, December 17, 2003 10:57 AM
To: [log in to unmask]
Subject: [TN] Need a chemist or chemical engineer to answer


Technetters,
It has been almost 30 years since I took kinetics.  I have dug out my old text books, but they only help so much. I'm a preparative inorganic chemist by training. My question is the following:  If a single compound sublimes, without decomposition, would you expect the kinetics to be zero or first order?  Thanks.
Bev Christian
Research in Motion

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