Units amount of substance

Base SI units Amount of substance mole mol Amount of substance which contains as many specified entities as there are atoms of carbon-12 in exactly 0.012 kg of that nuclide. The elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles. 

The SI unit for heat capacity is J-K k Molar heat capacities (Cm) are expressed as the ratio of heat supplied per unit amount of substance resulting in a change in temperature and have SI units of J-K -moC (at either constant volume or pressure). Specific heat capacities (Cy or Cp) are expressed as the ratio of heat supplied per unit mass resulting in a change in temperature (at constant volume or pressure, respectively) and have SI units of J-K -kg . Debye s theory of specific heat capacities applies quantum theory in the evaluation of certain heat capacities. 

If the reference materials are pure substances and can be specified on the microscopic level, then they represent the unit amount of substance. Because there are no absolute pure substances the representation is in all cases an approximation. The degree of approximation is given by the accuracy of the contents of the main component. In case of pure elements, e.g. metals Fe, Cu, Zn the determination of the main component by coulometry is limited by an uncertainty of 0.01%. The determination of all impurities needs completeness and requires a great deal of analytical equipment. However, a combination of inductively coupled plasma-mass spectrometry (ICP-MS), atomic absorption spectrometry (AAS) and isotope dilution mass spectrometry (ID-MS) covering all elements of the periodic table allows a decrease of total uncertainty to 0.0032% (Cu, see Fig. 8). 

Factors affected by the rate of pressure increase in a given space and for a given amount of energy include the pressure reached at equilibrium per unit amount of substance, and the reaction rate (or deflagration rate). The improved time/pressure test method is considered to be the test method that satisfies both constraints. In the case of having a clear flame front like KCIO 3 /cellulose mixtures, the deflagration rate can be obtained by the method discussed above. 

The mole is the amount of substance of a system that contains as many elementary entities as there are atoms in 0.012 kg of carbon-12. Although it is defined in terms of the number of entities, in practice, 1 mol of atoms, molecules, or specific formula units of a substance is measured by weighing M x (1 mol) of the substance, where M is the molar mass, the mass per unit amount of substance. Molar mass is synonymous with the terms atomic weight, for atoms, and molecular weight, for molecules or formula units, respectively, and is reported in grams per mole (g mol ). 

It is not necessary for every molecule of a compound to be radioactive for us to use the radioactivity as a measure of concentration (and, thereby, determine reaction rates, and so on). All that is necessary is that the sample contain enough radioactive molecules to count accurately and that we know the specific activity of the compound. Specific activity (S.A.) refers to the amount of radioactivity per unit amount of substance. It is, in fact, a way of designating the fraction of the total molecules present that is radioactive. Specific activity may be given in terms of curies per gram (Ci/g), millicuries... 

The specific latent heat (symbol Ij is the heat absorbed or released per unit mass of a substance in the course of its isothermal change of phase. The molar latent heat is the heat absorbed or released per unit amount of substance during an isothermai change of state. 

Conversions for energy/unit amount of substance, dimensions ML /T ... 

Replacing the volume by the molar volume of the gas, = Yin, i.e., the volume per unit amount of substance expressed in m moT , we obtain the condensed equation of state of ideal gases ... 

The chemical potential of a component of a phase is thus the amount by which the capacity of the phase for doing work (other than work of expansion) is increased per unit amount of substance added, for an infinitesimal addition at constant temperature and pressure. For example, the chemical potential of copper sulphate in its aqueous solution in a Daniell cell is equal to the increased capacity of the cell to provide electrical energy, per unit amount of copper sulphate added (the addition actually being an infinitesimal). 

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