ABSTRACT We present a physico-chemical approach to modeling the evolution of the universe based on a theory that space consists of energy quanta that constitute the cosmic fluid. The universe started from a subatomic size volume of an ideal gas at very high temperature and pressure. Upon expansion and cooling, phase transitions occurred resulting in the formation of fundamental particles, and matter. These nucleate and grow into stars, galaxies, and clusters through gravity. From the cooling curve of the universe and its thermodynamic phase diagram we made a correlation between dark energy and the energy of space. Using Friedmann’s equations, our model fits well WMAP data on cosmic composition with an equation of state parameter,w=-0.7. The expansion of the universe is better attributed to Quintessence than to a cosmological constant. Dark Matter is identified as a plasma form of matter similar to that which existed during the photon epoch. The thermodynamics of expansion of the universe was adiabatic and decelerating for most its first 7 billion years; it became accelerating upon the dominance of Dark Energy. The behavior of the observable universe fits well our Quantum Space model for a closed system, with a negative pressure for Dark Energy and provides a mechanism for the accelerated expansion due to gravitational attraction. The model is simpler than the Standard Model of Cosmology; it avoids the problem of singularity and does not need a theory of Inflation. The ultimate fate of the universe appears to be a Big Freeze.