Kinetic study of the reactions Br+IBr→I+Br2 and I+Br2→Br+IBr

The kinetics of the title reactions have been studied using the discharge-flow mass spectrometic method at 296 K and 1 torr of helium. The rate constant obtained for the forward reaction Br + IBr --> 1 + Br-2 (1), using three different experimental approaches (kinetics of Br consumption in excess of IBr, IBr consumption in excess of Br, and I formation), is: k(1) = (2.7 +/- 0.4) X 10(-11) cm(3) molecule(-1)s(-1). The rate constant of the reverse reaction: I + Br-2 --> Br + IBr (-1) has been obtained from the Br-2 consumption rate (with an excess of 1 atoms) and the IBr formation rate: k(-1) = (1.65 +/- 0.2) X 10(-13) cm(3)molecule(-1)s(-1). The equilibrium constant for the reactions (1,-1), resulting from these direct determinations of k(1) and k(-1) and, also, from the measurements of the equilibrium concentrations of Br, IBr, I, and Br-2, is: K-1 = k(1)/k(-1) = 161.2 +/- 19.7. These data have been used to determine the enthalpy of reaction (1), Delta H(298)degrees = -(3.6 +/- 0.1) kcal mol(-1) and the heat of formation of the IBr molecule, Delta H(f,298)degrees(IBr) = (9.8 +/- 0.1) kcal mol(-1). (C) 1998 John Wiley & sons, Inc.