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The molar gas constant (also known as the gas constant, universal gas constant, or ideal gas constant) is denoted by the symbol R or R. It is the molar equivalent to the Boltzmann constant , expressed in units of energy per temperature increment per amount of substance , rather than energy per temperature increment per particle .
It is however easy to convert the parameters to different pressure and temperature units. For switching from degrees Celsius to kelvin it is sufficient to subtract 273.15 from the C parameter. For switching from millimeters of mercury to pascals it is sufficient to add the common logarithm of the factor between both units to the A parameter:
The constant-volume gas thermometer works on the basis of the pressure-temperature law: when the volume of a gas is kept constant, its pressure is directly proportional its temperature. That is, Plots of pressure vs temperature for three different gas samples extrapolate to absolute zero.
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 ...
In gas dynamics we are interested in the local relations between pressure, density and temperature, rather than considering a fixed quantity of gas. By considering the density ρ = M / V {\displaystyle \rho =M/V} as the inverse of the volume for a unit mass, we can take ρ = 1 / V {\displaystyle \rho =1/V} in these relations.
Most scientists measure temperature using the Celsius scale and thermodynamic temperature using the Kelvin scale, which is the Celsius scale offset so that its null point is 0 K = −273.15 °C, or absolute zero. Many engineering fields in the US, notably high-tech and US federal specifications (civil and military), also use the Kelvin and ...
The theoretical temperature is determined by extrapolating the ideal gas law; by international agreement, absolute zero is taken as 0 kelvin (International System of Units), which is −273.15 degrees on the Celsius scale, [1] [2] and equals −459.67 degrees on the Fahrenheit scale (United States customary units or imperial units). [3]
It is as important to indicate the applicable reference conditions of temperature and pressure when stating the molar volume of a gas [48] as it is when expressing a gas volume or volumetric flow rate. Stating the molar volume of a gas without indicating the reference conditions of temperature and pressure has very little meaning and can cause ...