Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

The standard molar enthalpy of formation, molar heat capacities, and thermal stability of anhydrous caffeine

Dong, J.-X.[Jia-Xin], Li, Q.[Qiang], Tan, Z.-C.[Zhi-Cheng], Zhang, Z.-H.[Zhi-Heng], Liu, Y.[Yi]
J. Chem. Thermodyn. 2007, 39, 1, 108-114
ABSTRACT
The constant-volume energy of combustion of crystalline anhydrous caffeine (C8H10N4O2) in a (lower temperature steady) crystal form was measured by a bomb combustion calorimeter, the standard molar enthalpy of combustion of caffeine at T = 298.15 K was determined to be (4255.08 +- 4.30) kJ Ae mol 1, and the standard molar enthalpy of formation was derived as (322.15 +- 4.80) kJ Ae mol 1. The heat capacity of caffeine in the same crystal form was measured in the temperature range from (80 to 387) K by an adiabatic calorimeter. No phase transition or thermal anomaly was observed in the above temperature range. The thermal behavior of the compound was further examined by thermogravimetry (TG), differential thermal analysis (DTA) over the range from (300 to 700) K and by differential scanning calorimetry (DSC) over the range from (300 to 540) K, respectively. From the above thermal analysis a (solid solid) and a (solid liquid) phase transition of the compound were found at T = (413.39 and 509.00) K, respectively; and the corresponding molar enthalpies of these transitions were determined to be (3.43 +- 0.02) kJ Ae mol 1for the (solid solid) transition, and (19.86 +- 0.03) kJ Ae mol 1 for the (solid liquid) transition, respectively.
Compounds
# Formula Name
1 CO2 carbon dioxide
2 N2 nitrogen
3 H2O water
4 O2 oxygen
5 C8H10N4O2 caffeine
Datasets
The table above is generated from the ThermoML associated json file (link above). POMD and RXND refer to PureOrMixture and Reaction Datasets. The compound numbers are included in properties, variables, and phases, if specificied; the numbers refer to the table of compounds on the left.
Type Compound-# Property Variable Constraint Phase Method #Points
  • POMD
  • 5
  • Molar enthalpy of transition or fusion, kJ/mol ; Crystal 2
  • Crystal 2
  • Crystal 1
  • Air at 1 atmosphere
  • DSC:UFactor:4
  • 1
  • POMD
  • 5
  • Molar enthalpy of transition or fusion, kJ/mol ; Crystal 1
  • Crystal 1
  • Liquid
  • Air at 1 atmosphere
  • DSC:UFactor:2
  • 1
  • POMD
  • 5
  • Triple point temperature, K ; Crystal 1
  • Crystal 1
  • Liquid
  • Air at 1 atmosphere
  • DTA:UFactor:2
  • 1
  • POMD
  • 5
  • Triple point temperature, K ; Crystal 2
  • Crystal 2
  • Crystal 1
  • Air at 1 atmosphere
  • DTA:UFactor:2
  • 1
  • POMD
  • 5
  • Molar heat capacity at constant pressure, J/K/mol ; Crystal 2
  • Temperature, K; Crystal 2
  • Pressure, kPa; Crystal 2
  • Crystal 2
  • SMALLAD:UFactor:3
  • 116
  • RXND
  • 5
  • 1
  • 2
  • 3
  • 4
  • Molar internal energy of reaction at constant volume, kJ/mol
  • Rotating bomb calorimetry
  • 1