measurement of quantity mass and length of the substance or object it also refer a unit which help to measure the substance or object. true or false ?
Answers
In chemistry, the amount of substance in a given sample of matter is defined as the number of discrete atomic-scale particles in it divided by the Avogadro constant NA. In a truly atomistic view, the amount of substance is simply the number of particles that constitute the substance.[1][2][3] The particles or entities may be molecules, atoms, ions, electrons, or other, depending on the context. The value of the Avogadro constant NA has been defined as 6.02214076×1023 mol−1. In the truly atomistic view, 1 mol = 6.02214076×1023 particles (the Avogadro number) [4] and therefore the conversion constant is simply NA = 1.[3] The amount of substance is sometimes referred to as the chemical amount.
The mole (symbol: mol) is a unit of amount of substance in the International System of Units, defined (since 2019) by fixing the Avogadro constant at the given value. Historically, the mole was defined as the amount of substance in 12 grams of the carbon-12 isotope. As a consequence, the mass of one mole of a chemical compound, in grams, is numerically equal (for all practical purposes) to the mass of one molecule of the compound, in daltons, and the molar mass of an isotope in grams per mole is equal to the mass number. For example, a molecule of water has a mass of about 18.015 daltons on average, whereas a mole of water (which contains 6.02214076×1023 water molecules) has a total mass of about 18.015 grams.
In chemistry, because of the law of multiple proportions, it is often much more convenient to work with amounts of substances (that is, number of moles or of molecules) than with masses (grams) or volumes (liters). For example, the chemical fact "1 molecule of oxygen (O
2) will react with 2 molecules of hydrogen (H
2) to make 2 molecules of water (H
2O)" can also be stated as "1 mole of O
2 will react with 2 moles of H
2 to form 2 moles of water". The same chemical fact, expressed in terms of masses, would be "32 g (1 mole) of oxygen will react with approximately 4.0304 g (2 moles of H
2) hydrogen to make approximately 36.0304 g (2 moles) of water" (and the numbers would depend on the isotopic composition of the reagents). In terms of volume, the numbers would depend on the pressure and temperature of the reagents and products. For the same reasons, the concentrations of reagents and products in solution are often specified in moles per liter, rather than grams per liter.
The amount of substance is also a convenient concept in thermodynamics. For example, the pressure of a certain quantity of a noble gas in a recipient of a given volume, at a given temperature, is directly related to the number of molecules in the gas (through the ideal gas law), not to its mass.
This technical sense of the term "amount of substance" should not be confused with the general sense of "amount" in the English language. The latter may refer to other measurements such as mass or volume,[5] rather than the number of particles. There are proposals to replace "amount of substance" with more easily-distinguishable terms, such as enplethy[6] and stoichiometric amount.[5]
The IUPAC recommends that "amount of substance" should be used instead of "number of moles", just as the quantity mass should not be called "number of kilograms".[7]