The standard sublimation enthalpies for uracil, 1-methyluracil, 3-methyluracil, and 1,3-dimethyluracil, ∆ sub H°(298 K) ) (128 ( 2), (124 ( 5), (121 ( 4), and (118 ( 4) kJ mol -1 , respectively, were determined from their vapor pressures measured by the torsion method. The results of vapor pressure measurements were fit to the following linear equations: uracil, log(p/kPa) ) (12.29 ( 0.15) -(6634 ( 100) K/T (from 384 K to 494 K); 1-methyluracil, log(p/kPa) ) (13.75 ( 0.15) -(6357 ( 150) K/T (from 343 K to 428 K); 3-methyluracil, log(p/kPa) ) (13.59 ( 0.10) -(6210 ( 100) K/T (from 344 K to 419 K); 1,3-dimethyluracil, log(p/kPa) ) (15.10 ( 0.10) -(6049 ( 100) K/T (from 311 K to 364 K). The different sublimation behavior of some compounds can be due to the presence of hydrogen bonds in their solid state.
The vapor pressures of DyCl3, DyBr3, and DyI3 were measured by the torsion method, and the following
selected equations were derived in the covered temperature ranges. DyCl3: log(p/kPa) = 9.31 ± 0.30 −
(12523 ± 300)(K/T), (924−1214 K). DyBr3: log(p/kPa) = 11.47 ± 0.30 − (14344 ± 300)(K/T), (878−1151
K). DyI3: log(p/kPa) = 11.34 ± 0.20 − (13800 ± 200)(K/T), (889−1157 K). Treating by second- and third-law methods the obtained results, the standard sublimation enthalpies, Δsub
H°(298 K) = 283 ± 5, 289 ±
6, and 282 ± 4 kJ mol-1 for DyCl3, DyBr3, and DyI3, respectively, were determined.
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