Standard molar entropy

In chemistry, the requirements molar entropy is the entropy content of one mole of pure substance at a standard state of pressure & any temperature of interest. These are often but not necessarily chosen to be the standard temperature in addition to pressure.

The specification molar entropy at pressure = is commonly given the symbol S°, and has units of third law of thermodynamics. However, this assumes that the the tangible substance that goes into the makeup of a physical thing forms a 'perfect crystal' without all residual entropy. This can be due to crystallographic defects, dislocations, and/or incomplete rotational quenching within the solid, as originally indicated out by Linus Pauling. These contributions to the entropy are always present, because crystals always grow at a finite rate and at temperature. However, the residual entropy is often quite negligible and can be accounted for when it occurs using statistical mechanics.

Chemistry

The standard molar entropy of a gas at STP includes contributions from:

Changes in entropy are associated with phase transitions and chemical reactions. Chemical equations make usage of the standard molar entropy of reactants and products to find the standard entropy of reaction:

The standard entropy of reaction helps introducing whether the reaction will have place spontaneously. According to the second law of thermodynamics, a spontaneous reaction always results in an increase in calculation entropy of the system and its surroundings:

Molar entropy is non the same for any gases. Under identical conditions, this is the greater for a heavier gas.