Rate coefficients (k(-7)) for the thermal decomposition of bromine nitrate, BrONO2 + M --> BrO + NO2 + M, have been obtained at temperatures between 320 and 340 K and pressures between 100 and 1000 Torr. These data are combined with recommended values for the reverse reaction to obtain an equilibrium constant for the reaction pair, K-P.7 = 5.44 x 10(-9) exp(14192/T) atm(-1), and a heat of reaction for the thermal dissociation of 28.2 +/- 1.5 kcal/mol at 298 K. This reaction enthalpy is used in conjunction with literature data to arrive at a consistent set of Delta H-f degrees(298 K) data for BrONO2 (10.1 +/- 2.0 kcal/mol), BrO (30.4 +/- 2.0 kcal/mol), HOBr (-14.1 +/- 2.0 kcal/mol), and Br2O (27.3 +/- 2.0 kcal/mol). Additional measurements were made to determine the rate coefficient for Br atom reaction with BrONO2 (k(11)) relative to the rate coefficient for its reaction with CH3CHO (k(12)) at 298 K : k(11)/k(12) = 12.5 +/- 0.6. This relative rate measurement yields a rate coefficient of (4.9 +/- 1.5) x 10(-11) cm(3) molecule(-1) s(-1) for k(11), using the currently recommended value for k(12). Approximate rate constants for reaction of NO (reaction 17) and BrNO (reaction 19) with BrONO2 were also obtained : k(17) = 3 x 10(-19) cm(3) molecule(-1) s(-1), k(19) > 1 x 10(-16) cm(3) molecule(-1) s(-1).