Thermodynamics of monoclinic Fe2(SO4)3

Juraj Majzlan, Alexandra Navrotsky, Rebecca Stevens, Marcus Donaldson, Brian F. Woodfield, Juliana Boerio-Goates

Research output: Contribution to journalArticlepeer-review

21 Scopus citations

Abstract

Thermodynamic properties of monoclinic Fe2(SO4) 3 were measured by acid solution calorimetry, adiabatic calorimetry, and semi-adiabatic calorimetry. The standard molar enthalpy of formation ΔfHm° was determined as -(2585.2 ± 4.9) kJ • mol -1 by an appropriate thermochemical cycle with enthalpies of solution of monoclinic Fe2(SO4)3, α-MgSO 4, γ-FeOOH, H2O, and MgO in 5 N HCl at T = 298 K. Heat capacity data were collected from T = (0.5 to 400) K. The standard molar entropy Sm° at T = 298.15 K is (305.6 ± 0.6) J • K-1 • mol-1. While the enthalpy of formation agrees well with a previous ΔfHm° determination, the entropy differs significantly because magnetic entropy was entirely overlooked in the previous work. The heat capacity shows a sharp magnetic transition with the peak located at 30.0 K. The Cp,m data in the temperature range (273 to 395) K are represented by a Maier-Kelley polynomial Cp,m/J • K-1 • mol-1 = 213.0 + 0.3121(T/K) - 2.959 × 106(T/K) -2. The calculated standard molar Gibbs free energy of formation from the elements ΔfGm° at T = 298.15 K is -(2264.5 ± 4.9) kJ • mol-1.

Original languageEnglish (US)
Pages (from-to)802-809
Number of pages8
JournalJournal of Chemical Thermodynamics
Volume37
Issue number8
DOIs
StatePublished - Aug 2005
Externally publishedYes

Keywords

  • Entropy
  • Heat capacity
  • Heat of formation
  • Magnetic transition
  • Monoclinic iron(III) sulfate

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Materials Science(all)
  • Physical and Theoretical Chemistry

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