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In chemistry, the standard molar entropy is the entropy content of one mole of substance, under conditions of standard temperature and pressure. By comparing the entropies S and enthalpies H of products and reactants in a chemical reaction, we can determine whether the reaction will go forward or backwards. If the Gibbs free energy (G = H - TS) is negative, the forward reaction will take place. The standard molar entropy is usually given the symbol S0, and the units J/(mol·K) (joules per mole-kelvin). Chemistry (in Greek: χημεία) is the science of matter that deals with the composition, structure, and properties of substances and with the transformations that they undergo. ... Jump to: navigation, search In thermodynamics and statistical mechanics, the thermodynamic entropy (or simply the entropy) S is a measure of the internal microscopic disorder present in a system at thermodynamic equilibrium; or, equivalently, the number of possible internal configurations available to the system. ... Jump to: navigation, search The mole (symbol: mol) is the SI base unit of the amount of particulate substance. ... Temperature and air pressure can vary from one place to another on the Earth, and can also vary in the same place with time. ... Jump to: navigation, search In thermodynamics the Gibbs free energy is a state function of any system defined as G = H − T·S where G is the Gibbs free energy, measured in joules H is the enthalpy, measured in joules T is the temperature, measured in kelvins S is the... Jump to: navigation, search The joule (symbol: J) is the SI unit of energy, or work. ... Jump to: navigation, search The mole (symbol: mol) is the SI base unit of the amount of particulate substance. ... Jump to: navigation, search The kelvin (symbol: K) is the SI unit of temperature, and is one of the seven SI base units. ...
Entropy is related to the energy distribution of energy states of a collection of molecules, and this aspect is usually discussed in statistical mechanics.
Entropy is also related to probability, as a measure of randomness or disorder, and entropy is proportional to the logarithm of the probability.
Since the entropies of most substances have been measured and tabulated in handbooks and data banks, standardentropies of reactions can be evaluated in a similar manner as enthalpies of reactions.
The standardmolarentropy is simply the entropy of 1 mol of a pure substance at 1 atm pressure and standard temperature (usually 25°C).
Both entropy and enthalpy considerations are combined in the term free energy change (abbreviated ΔG), which is the ultimate criterion for determining the spontaneity of a reaction.
The standard free energy of formation of a substance measures its thermodynamic stability with respect to its constituent elements.
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