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  2. Entropy - Wikipedia

    en.wikipedia.org/wiki/Entropy

    Since an entropy is a state function, the entropy change of the system for an irreversible path is the same as for a reversible path between the same two states. [22] However, the heat transferred to or from the surroundings is different as well as its entropy change. We can calculate the change of entropy only by integrating the above formula.

  3. Hess's law - Wikipedia

    en.wikipedia.org/wiki/Hess's_law

    If the enthalpy changes are known for all the equations in the sequence, their sum will be the enthalpy change for the net equation. If the net enthalpy change is negative ( Δ H net < 0 {\displaystyle \Delta H_{\text{net}}<0} ), the reaction is exothermic and is more likely to be spontaneous ; positive Δ H values correspond to endothermic ...

  4. Entropy as an arrow of time - Wikipedia

    en.wikipedia.org/wiki/Entropy_as_an_arrow_of_time

    Entropy is one of the few quantities in the physical sciences that require a particular direction for time, sometimes called an arrow of time. As one goes "forward" in time, the second law of thermodynamics says, the entropy of an isolated system can increase, but not decrease. Thus, entropy measurement is a way of distinguishing the past from ...

  5. Entropy (order and disorder) - Wikipedia

    en.wikipedia.org/wiki/Entropy_(order_and_disorder)

    To highlight the fact that order and disorder are commonly understood to be measured in terms of entropy, below are current science encyclopedia and science dictionary definitions of entropy: A measure of the unavailability of a system's energy to do work; also a measure of disorder; the higher the entropy the greater the disorder. [4]

  6. Van 't Hoff equation - Wikipedia

    en.wikipedia.org/wiki/Van_'t_Hoff_equation

    The Van 't Hoff equation relates the change in the equilibrium constant, K eq, of a chemical reaction to the change in temperature, T, given the standard enthalpy change, Δ r H ⊖, for the process. The subscript r {\displaystyle r} means "reaction" and the superscript ⊖ {\displaystyle \ominus } means "standard".

  7. Introduction to entropy - Wikipedia

    en.wikipedia.org/wiki/Introduction_to_entropy

    The entropy of the surrounding room decreases less than the entropy of the ice and water increases: the room temperature of 298 K is larger than 273 K and therefore the ratio, (entropy change), of ⁠ δQ / 298 K ⁠ for the surroundings is smaller than the ratio (entropy change), of ⁠ δQ / 273 K ⁠ for the ice and water system. This is ...

  8. Nernst heat theorem - Wikipedia

    en.wikipedia.org/wiki/Nernst_heat_theorem

    The above equation is a modern statement of the theorem. Nernst often used a form that avoided the concept of entropy. [1] Graph of energies at low temperatures. Another way of looking at the theorem is to start with the definition of the Gibbs free energy (G), G = H - TS, where H stands for enthalpy.

  9. Sackur–Tetrode equation - Wikipedia

    en.wikipedia.org/wiki/Sackur–Tetrode_equation

    The Sackur–Tetrode equation is an expression for the entropy of a monatomic ideal gas. [ 1 ] It is named for Hugo Martin Tetrode [ 2 ] (1895–1931) and Otto Sackur [ 3 ] (1880–1914), who developed it independently as a solution of Boltzmann's gas statistics and entropy equations, at about the same time in 1912.