Avogadro s constant

N. is Avogadro s constant. The most commonly used unit then is cm s sometimes inconsistently written — 1... 

In electrochemistry it is customary to multiply each of those quantities by Avogadro s constant and, when a few additional ions enter the already saturated solution, to speak of the entropy of solution per mole. Let the entropy of one mole of the crystalline solid be denoted by Scr and let Si and S2 denote, respectively, the entropy of the solution before, and after, the entry of the additional solute, both expressed in calories per mole. The total initial entropy is obviously (S + Si) and the final entropy is St. The difference between the final and the initial entropy is by definition AS,at. 

In the case of a sparingly soluble substance, if each of the quantities in (64) is divided by Avogadro s constant, we confirm the statement made above— namely, that, if AS at per ion pair is added to the contribution made to the entropy of the crystal by each ion pair, in this way we evaluate the contribution made by one additional ion pair to the entropy of the saturated solution and it is important to grasp that this contribution depends only on the presence of the additional pair of ions in the solution and does not depend on where they have come from. They might have been introduced into the solution from a vacuum, instead of from the surface of a solid. In (64) the quantities on the right-hand side refer to the solution of a crystal, but the quantity (S2 — Si) does not it denotes merely a change in the entropy of a solution due to the presence of additional ions, which may have come from anywhere. When Si denotes the entropy of a sufficiently large amount of solution, (S2 — Si) is the partial molal entropy of the solute in this solution. 

Since in the various processes considered the quantities L, D, Y, and J form the unitary part of AF, we sec that, in these various processes, ASuniion, is either equal to — (dL/dT) or — (dD/dT) or — (dY/dT) or — (dJ/dT) (multiplied in each case by Avogadro s constant to give the value per mole). 

In discussing the proton transfer (66), we saw that one of the neutral species could be a solvent molecule. We shall discuss that case below. Here we may notice that, when all four species are solute particles, the number of solute particles is unchanged by the reaction, or Aq = 0. In such a case AF° happens to be equal to the characteristic unit U multiplied by Avogadro s constant. 

Finally, multiplying by Avogadro s constant, and subtracting from both sides the constant quantity 2RT In M, we obtain, since y — m/M... 

The entropy per molecule of liquid water will therefore be 16.75 e.u., divided by Avogadro s constant. We have next to consider the change of entropy when a proton is added to a water molecule to give an (II30)+ ion. It is this quantity that is arbitrarily put equal to zero in Latimer s scale. We see at once that the value that must be allotted to the (HaO)+ ion in Latimer s list is 16.75 e.u. 

The molecular weight of H2O being 18.0, 1 mole of water at room temperature occupies 18.0 cm. If several water molecules are added to a quantity of water, the increment in volume per molecule added will be 18.0 cm3 divided by Avogadro s constant. In other words, omitting Avogadro s constant, the increment will be 18.0 cms/mole. As we shall be interested in ion pairs, we may remark that the increment in volume per pair of H2O molecules will be 3G cma/mole and we may use this value as a basis of comparison for a pair of atomic ions. 

In the uni-divalent or di-univalent solute, to which (181) refers, n is equal to 3, and (182), when multiplied by Avogadro s constant, takes the form... 

The number of objects per mole, 6.0221 X 1023 mol-1, is called Avogadro s constant, NA, in honor of the nineteenth-century Italian scientist Amedeo Avo-gadro (Fig. E.3), who helped to establish the existence of atoms. Avogadro s constant is used to convert between the chemical amount (the number of moles) and the number of atoms, ions, or molecules in that amount ... 

Number of objects = amount in moles X number of objects per mole = amount in moles X Avogadro s constant... 

A note on good practice Avogadro s constant is a constant with units, not a pure number. You will often hear people referring to Avogadro s number-, they mean the pure number 6.0221 X 1023. 

The amounts of atoms, ions, or molecules in a sample are expressed in moles, and Avogadro s constant, NA, is used to convert between numbers of these particles and the numbers of moles. 

The molar masses of elements are determined by using mass spectrometry to measure the masses of the individual isotopes and their abundances. The mass per mole of atoms is the mass of an individual atom multiplied by Avogadro s constant (the number of atoms per mole) ... 

STRATEGY First calculate the average atomic mass of the isotopes by adding together the individual masses, each multiplied by the fraction that represents its abundance. Then obtain the molar mass, the mass per mole of atoms, by multiplying the average atomic mass by Avogadro s constant. 

Use Avogadro s constant to convert between amount in moles and the number of atoms, molecules, or ions in a sample (Examples E.l and E.2). 

In the last step, we have used the relation 1— + f — +. .. = ln2. Finally, we multiply T. by 2 to obtain the total energy arising from interactions on each side of the ion and then by Avogadro s constant, NA, to obtain an expression for the potential energy per mole of ions. The outcome is... 

The total number of molecules, N, is the product of the amount, n, and Avogadro s constant, NA so the last equation becomes... 

STRATEGY We calculate the density of the metal by assuming first that its structure is ccp (fee) and then that it is bcc. The structure with the density closer to the experimental value is more likely to be the actual structure. The mass of a unit cell is the sum of the masses of the atoms that it contains. The mass of each atom is equal to the molar mass of the element divided by Avogadro s constant. The volume of a cubic unit cell is the cube of the length of one of its sides. That length is obtained from the radius of the metal atom, the Pythagorean theorem, and the geometry of the cell. 

The work done when an amount n of electrons (in moles) travels through a potential difference E is their total charge times the potential difference. The charge of one electron is — e the charge per mole of electrons is eNA, where NA is Avogadro s constant. Therefore, the total charge is —neNA and the work done is... 

Faraday s constant, F, is the magnitude of the charge per mole of electrons (the product of the elementary charge e and Avogadro s constant NA) ... 

Ligand field splittings are normally reported as a molar energy, and so we need to multiply this expression by Avogadro s constant ... 

Avogadro s constant The number of objects per mole of objects (Na = 6.022 14 X 102 mol ). Avogadro s number is the number of objects in one mole of objects (that is, the dimensionless number 6.022 14 XlO2 ). Avogadro s principle The volume of a sample of gas at a given temperature and pressure is proportional to the amount of gas molecules in the sample V n. axial bond A bond that is perpendicular to the molecular plane in a bipyramidal molecule, axial lone pair A lone pair lying on the axis of a bipyramidal molecule. 

Avogadro, A., F39, 144 Avogadro s constant, F39 Avogadro s number, F39 Avogadro s principle, 38,... 

In (3) N is Avogadro s constant, r the radius of a conducting sphere, Z the charge number, and e the elementary electric charge. 

If no side reactions occur at the electrode that would participate in the overall current flow, then the Faraday law can be used not only to measure the charge passed (i.e. in coulometres see Section 5.5.4) but also to define the units of electric current and even to determine Avogadro s constant. 

Avogadro s constant Rg = universal gas constant M = molecular weight tf) = constant... 

---