Heat capacity from 12 to 305°K and entropy of talc and tremolite

Abstract

The heat capacities of talc, Mg 3 Si 4 O 10 (OH) 2 , and tremolite, Ca 2 Mg 6 Si 8 O 22 (OH) 2 , have been measured between 12 and 305°K. Smoothed values of heat capacity, entropy, enthalpy, and free energy are tabulated. At 298.15° K. the values of the thermodynamic functions are: talc, C p °= 76.89 ± 0.23 cal. deg. -1 mole -1 , S° = 62.33 ± 0.19 cal. deg. -1 mole -1 , H° - H 0 ° = 11,206 ± 34 cal. mole -1 ; tremolite, Cp° = 156.7 ± 0.6 cal. deg. -1 mole -1 , S° = 131.2 ± 0.5 cal. deg. -1 mole -1 , H° - H 0 ° = 23,335 ± 90 cal. mole -1 . From the equilibrium data of Bowen and Tuttle and the entropy of talc, the heat of formation of talc from MgO, SiO 2 , and H 2 O (liq.) is calculated to be Δ H°f 298 = -43.6 ± 1 kcal.