Kinetic parameters for the dominant pathways during the addition of the four Si2H2 isomers, i.e., trans-HSiSiH, SiSiH2, Si(H)SiH, and Si(H-2)Si, to monosilane, SiH4, and disilane, Si2H6, have been calculated using G3//B3LYP, statistical thermo dynamics, conventional and variational transition state theory, and internal rotation corrections. The direct addition products of the multifunctional Si2H2 isomers were monofunctional substituted silylenes, hydrogen bridged species, and silenes. During addition to monosilane and disilane, the SiSiH2 isomer was found to be most reactive over the temperature range of 800 to 1200 K Revised parameters for the Evans -Polanyi correlation and a representative pre-exponential factor for multifunctional silicon hydride addition and elimination reaction families under pyrolysis conditions were regressed from the reactions in this study. This revised kinetic correlation was found to capture the activation energies and rate coefficients better than the current literature methods.