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In physics, the thermal equation of state is a mathematical expression of pressure P, temperature T, and, volume V.The thermal equation of state for ideal gases is the ideal gas law, expressed as PV=nRT (where R is the gas constant and n the amount of substance), while the thermal equation of state for solids is expressed as:
The equation modifies the ideal gas law in two ways: first, it considers particles to have a finite diameter (whereas an ideal gas consists of point particles); second, its particles interact with each other (unlike an ideal gas, whose particles move as though alone in the volume). The equation is named after Dutch physicist Johannes Diderik ...
The van der Waals equation of state is the simplest and best-known modification of the ideal gas law to account for the behaviour of real gases: (+ (~)) (~) =, where p is pressure, n is the number of moles of the gas in question and a and b depend on the particular gas, ~ is the volume, R is the specific gas constant on a unit mole basis and T ...
The ideal gas equation can be rearranged to give an expression for the molar volume of an ideal gas: = = Hence, for a given temperature and pressure, the molar volume is the same for all ideal gases and is based on the gas constant: R = 8.314 462 618 153 24 m 3 ⋅Pa⋅K −1 ⋅mol −1, or about 8.205 736 608 095 96 × 10 −5 m 3 ⋅atm⋅K ...
Isotherms of an ideal gas for different temperatures. The curved lines are rectangular hyperbolae of the form y = a/x. They represent the relationship between pressure (on the vertical axis) and volume (on the horizontal axis) for an ideal gas at different temperatures: lines that are farther away from the origin (that is, lines that are nearer to the top right-hand corner of the diagram ...
The cubic virial equation of state at is: = (+ +) It can be rearranged as: (+ +) = The factor / is the volume of saturated gas according to the ideal gas law, and can be given a unique name : = In the saturation region, the cubic equation has three roots, and can be written alternatively as: () = which can be expanded as: (+ +) + (+ +) = is a ...
Proposed in 1873, the van der Waals equation of state was one of the first to perform markedly better than the ideal gas law. In this equation, usually is called the attraction parameter and the repulsion parameter (or the effective molecular volume). While the equation is definitely superior to the ideal gas law and does predict the formation ...
His new formula revolutionized the study of equations of state, and was the starting point of cubic equations of state, which most famously continued via the Redlich–Kwong equation of state [7] and the Soave modification of Redlich-Kwong. [8] The van der Waals equation of state can be written as