We measure the expansion of the forward shock of the Small Magellanic Cloud supernova remnant 1E,0102.2-7219 in X-rays using Chandra X-Ray Observatory on-axis Advanced CCD Imaging Spectromete(ACIS) observations from 1999-2016. We estimate an expansion rate of 0.025%pm0.006%yr^{-1} and a blast-wave velocity of 1.61pm0.37times10^3 km s^{-1}. Assuming partial electron-ion equilibration via Coulomb collisions and cooling due to adiabatic expansion, this velocity implies a postshock electron temperature of 0.84pm0.20 keV which is consistent with the estimate of 0.68pm0.05 keV based on the X-ray spectral analysis. We combine the expansion rate with the blast wave and reverse shock radii to generate a grid of one-dimensional models for a range of ejecta masses (2-6 msol) to constrain the explosion energy, age, circumstellar density, swept-up mass, and unshocked-ejecta mass. We find acceptable solutions for a constant density ambient medium and for an r^{-2} power-law profile (appropriate for a constant progenitor stellar wind). For the constant density case, we find an age of sim 1700 yr, explosion energies 0.87-2.61times10^{51} erg, ambient densities 0.85-2.54 amu cm^{-3}, swept-up masses 22-66 msol, and unshocked-ejecta masses 0.05-0.16 msol. For the power-law density profile, we find an age of sim 2600 yr, explosion energies 0.34-1.02times10^{51} erg, densities 0.22-0.66 amu cm^{-3} at the blast wave, swept-up masses 17-52 msol, and unshocked-ejecta masses 0.06-0.18 msol. Assuming the true explosion energy was 0.5-1.5times10^{51} erg, ejecta masses 2-3.5 msol are favored for the constant density case and 3-6 msol for the power-law case. The unshocked-ejecta mass estimates are comparable to Fe masses expected in core-collapse supernovae with progenitor mass 15.0-40.0 msol, offering a possible explanation for the lack of Fe emission observed in X-rays.
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