The chemical thermodynamic properties of isomer groups of monochloroalkanes from C2H5Cl to C8H1 7Cl in the ideal gas phase have been calculated from 298.15 to 1500 K using new Benson group values from Bozzelli. Increments in isomer group properties per CH2 have been calculated to show the extent to which thermodynamic properties of higher isomer groups may be obtained by linear extrapolation. Equilibrium mole fractions within isomer groups have been calculated for the ideal gas state. Values of C° p, S°, ÎfH°, and ÎfG are given for all species of monochloroalkanes from CH3Cl to C8H1 7Cl in SI units for a standard state pressure of 1 bar. The values calculated here are compared with values published by the Thermodynamics Research Center (Texas A&M University) on June 30, 1981. © 1990, American Institute of Physics for the National Institute of Standards and Technology. All rights reserved.