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In chemistry, the standard molar entropy is the entropy content of one mole of pure substance at a standard state of pressure and any temperature of interest. These are often (but not necessarily) chosen to be the standard temperature and pressure .
The molar entropy of ions is obtained as a difference in entropy from a reference state defined as zero entropy. The second law of thermodynamics states that the entropy of an isolated system must increase or remain constant.
Absolute entropy of strontium. The solid line refers to the entropy of strontium in its normal standard state at 1 atm pressure. The dashed line refers to the entropy of strontium vapor in a non-physical state. The standard entropy change for the formation of a compound from the elements, or for any standard reaction is designated ΔS° form or ...
So, the molar entropy of an ideal gas is given by (,) = (,) + . In this expression C P now is the molar heat capacity. The entropy of inhomogeneous systems is the sum of the entropies of the various subsystems.
If the amount of substance in moles can be determined, then each of these thermodynamic properties may be expressed on a molar basis, and their name may be qualified with the adjective molar, yielding terms such as molar volume, molar internal energy, molar enthalpy, and molar entropy. The symbol for molar quantities may be indicated by adding ...
The molar volume of a mixture can be found from the sum of the excess volumes of the components of a mixture: = (+ ¯). This formula holds because there is no change in volume upon mixing for an ideal mixture. The molar entropy, in contrast, is given by
In thermodynamics, Trouton's rule states that the (molar) entropy of vaporization is almost the same value, about 85–88 J/(K·mol), for various kinds of liquids at their boiling points. [1] The entropy of vaporization is defined as the ratio between the enthalpy of vaporization and the boiling temperature.
Std entropy change of vaporization, Δ vap S o crystal I → liquid 79.87 J/(mol·K) at −89.0 °C Std enthalpy change of state transition, Δ trs H o crystal II → crystal I 2.282 kJ/mol at −183.3 °C Std entropy change of state transition, Δ trs S o crystal II → crystal I 25.48 kJ/mol at −183.3 °C Solid properties Std enthalpy change