THERMOCHEMISTRY OF THE REACTION OF HYDROGEN-SULFIDE WITH IODINE AND THE HEAT OF FORMATION OF HSI - NEW SULFUR COMPOUND

Gas-phase equilibrium constants K for the reaction H2S +I2⇄ HSI + HI have been measured spectrophotometri-cally over the temperature range 519-596 K. From the measured values of K, ΔH°558 = 6.19 ± 0.57 kcal/mol and ΔS°558 = 1.6 ± 1.0 eu are obtained. When corrected to room temperature by using an estimated value ΔCp° = -0.3 ± 0.2 gibbs/mol, these become ΔH°298 = 6.28 ± 0.67 kcal/mol and ΔS°298 = 1.8 ± 1.2 eu. This yields values of ΔHf°298(HSI, g) = 10.08 ± 0.67 kcal/mol and S°298(HSI, g) = 64.3 ± 1.2 eu when combined with known values for H2S, I2, and HI. The above value of entropy agrees well with the estimated value. A tenfold slower secondary reaction leads to the formation of a new product which is probably SI2 or HS2I. © 1979, American Chemical Society. All rights reserved.