Thermodynamic properties of tricesium chromium(V) tetroxide (Cs 3CrO 4)

Abstract

Low-temperature and solution-calorimetric investigations of Cs 3CrO 4 have yielded the following thermodynamic properties at T = 298.15 K: S°=(296.2±1.5)JK -1mol -1, C° p=(179.9±0.5)JK -1mol -1,-{ G°( T- H°(0)}=(169.0±0.8)JK -1mol -1,{ H°(T)- H°(0)}=(37.912±0.114)kJ mol -1 and δ H° f=-(1543.13±2.66)kJ mol -1 An unusual feature of the solution calorimetry was the use of aqueous xenon trioxide, XeO 3(aq). as oxidant. High-temperature drop calorimetry revealed a solid-to-solid (β-to-γ) transition at 774 K with ΔH tr = 1.8 kJ mol −1 and ΔS tr = 2.3 J K −1 mol −1. Below the transition temperature. the enthalpy increment as a function of temperature is best represented by { H°(T)- H°(298.15K)}/J mol -1=-46804.3+135.625( T K )+6.633544×10 -2( T K ) 2+1.777146×10 -5( T K ) 3 ,and, above the transition, by { H°(T)- H°(298.15K)}/J mol -1=-38654.8+155.722( T K )+4.35257×10 -2( T K ) 2 A table of thermodynamic functions to 1000 K is given.