The change in entropy $\Delta S$ between an initial- and a final thermodynamic state of a system can be determined by calculating the integral of dQ/T for a reversible path between the initial final states.
It is interesting to note that $ΔH$ (enthalpy change) and $ΔS$ (entropy change) values for any chemical reaction remain nearly constant even on varying temperature.
Enthalpy is simply a useful derived property for analyzing certain type of thermodynamic problems. It is not a fundamental property such as internal energy, entropy, pressure, volume and temperature.
1 Internal energy and enthalpy. I am finding it hard to distinguish between the two. Confused. Can someone explain me the two terms and difference between them? I tried learning from wikipedia but it said for both the above terms that it is the total energy contained by a thermodynamic system, so Iam confused?
Entropy is the cumulative filling of energy destinations between absolute zero (motionless) and a given temperature. Heat capacity is the rate of change of entropy with temperature… scaled by temperature.
2 I'm curious about how entropy is defined within chaos theory. Are there analogous laws similar to the second law of thermodynamics? How do we define steady-state or equilibrium within the state space of a system governed by chaos theory? Is the dynamics considered reversible in principle?
1 We know that Nature tends to drive forward any process that would maximize entropy. The formation of reaction products that have a lower internal energy level than the reactants ($\Delta U<0$) seems promising, as the energy released could heat the surroundings, thus increasing the entropy of the rest of the universe.
As we increase the entropy going from the solid to liquid, we have to do so under the condition of no change in free energy, thus the enthalpy has to exactly match the entropic free energy TS.
Enthalpy is not just a mathematical intermediate step everytime. A reasonable definition of internal energy could be: Energy derived from completely annihilating a system. $ \Delta H = \Delta U + P\Delta V$ So, in a constant external pressure surrounding, enthalpy is the new internal energy. Chemists usually deal with complicated reactions where matter changes state multiple times. For example ...
