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Mariotte's bottle is a device that delivers a constant rate of flow from closed bottles or tanks. It is named after French physicist Edme Mariotte (1620-1684). A picture of a bottle with a gas inlet is shown in the works of Mariotte, [ 1 ] but this construction was made to show the effect of outside pressure on mercury level inside the bottle.
Barometer – a device which measures pressure, most notably atmospheric pressure. [3] An ideal gas barometer may be constructed by mechanically connecting an ideal gas to the system being measured, while thermally insulating it. The volume will then measure pressure, by the ideal gas equation P = NkT/V.
Entropy cannot be measured directly. The change in entropy with respect to pressure at a constant temperature is the same as the negative change in specific volume with respect to temperature at a constant pressure, for a simple compressible system. Maxwell relations in thermodynamics are often used to derive thermodynamic relations. [2]
where P is the pressure of the gas, V is the volume of the gas, and k is a constant for a particular temperature and amount of gas. Boyle's law states that when the temperature of a given mass of confined gas is constant, the product of its pressure and volume is also constant. When comparing the same substance under two different sets of ...
where V 100 is the volume occupied by a given sample of gas at 100 °C; V 0 is the volume occupied by the same sample of gas at 0 °C; and k is a constant which is the same for all gases at constant pressure. This equation does not contain the temperature and so is not what became known as Charles's Law.
The isothermal–isobaric ensemble (constant temperature and constant pressure ensemble) is a statistical mechanical ensemble that maintains constant temperature and constant pressure applied. It is also called the N p T {\displaystyle NpT} -ensemble, where the number of particles N {\displaystyle N\,} is also kept as a constant.
P = pressure V = volume n = number of moles R = universal gas constant T = temperature. The ideal gas equation of state can be arranged to give: = / or = / The following partial derivatives are obtained from the above equation of state:
where H is the enthalpy, T the absolute temperature and G the Gibbs free energy of the system, all at constant pressure p. The equation states that the change in the G/T ratio at constant pressure as a result of an infinitesimally small change in temperature is a factor H/T 2. Similar equations include [6]