Molecular weight designation and unit of measurement. How molar mass is measured. How to determine the mass of a molecule

In the international system of units (SI), a mole is taken as a unit of quantity of a substance.

Moth - This is the amount of a substance containing as many structural units (molecules, atoms, ions, electrons, etc.) as there are atoms in 0.012 kg of the carbon isotope 12 C.

Knowing the mass of one carbon atom (1.93310 -26 kg), one can calculate the number of atoms N A in 0.012 kg of carbon

N A = 0.012 / 1.93310 -26 = 6.0210 23 mol -1

6.0210 23 mol -1 is called Avogadro's constant(designation N A, dimension 1 / mol or mol -1). It shows the number of structural units in a mole of any substance.

Molar mass- a value equal to the ratio of the mass of a substance to the amount of a substance. It has a dimension of kg / mol or g / mol. Usually it is designated M.

In general, the molar mass of a substance, expressed in g / mol, is numerically equal to the relative atomic (A) or relative molecular weight (M) of this substance. For example, the relative atomic and molecular weights of C, Fe, O 2, H 2 O are respectively equal to 12, 56, 32, 18, and their molar masses are, respectively, 12 g / mol, 56 g / mol, 32 g / mol, 18 g / mol.

It should be noted that the mass and quantity of a substance are different concepts. Mass is expressed in kilograms (grams) and the amount of substance is expressed in moles. There are simple relationships between the mass of a substance (m, g), the amount of a substance (ν, mol) and molar mass (M, g / mol)

m = νM; ν = m / M; M = m / ν.

Using these formulas, it is easy to calculate the mass of a certain amount of a substance, or to determine the number of moles of a substance in a known mass, or to find the molar mass of a substance.

Relative atomic and molecular weights

In chemistry, not absolute values of masses are traditionally used, but relative ones. Since 1961, the atomic mass unit (abbreviated amu), which is 1/12 of the mass of the carbon-12 atom, that is, the carbon isotope 12C, has been accepted as a unit of relative atomic masses since 1961.

Relative molecular weight(M r) of a substance is a value equal to the ratio of the average mass of a molecule of the natural isotopic composition of a substance to 1/12 of the mass of a carbon atom 12 C.

The relative molecular mass is numerically equal to the sum of the relative atomic masses of all atoms that make up the molecule, and is easily calculated by the formula of the substance, for example, the formula of the substance B x D y C z, then

M r = xA B + yA D + zA C.

Molecular weight is measured in amu. and is numerically equal to the molar mass (g / mol).

Gas laws

The state of a gas is fully characterized by its temperature, pressure, volume, mass and molar mass. The laws that connect these parameters are very close for all gases, but absolutely exact for ideal gas , in which there is no interaction between the particles, and the particles of which are material points.

The first quantitative studies of the reactions between gases belong to the French scientist Gay-Lussac. He is the author of the laws on thermal expansion of gases and the law of volumetric relations. These laws were explained in 1811 by the Italian physicist A. Avogadro. Avogadro's law - one of the important basic provisions of chemistry, stating that “ equal volumes of different gases, taken at the same temperature and pressure, contain the same number of molecules».

Consequences from Avogadro's law:

1) the molecules of most simple atoms are diatomic (H 2 , O 2 etc.);

2) the same number of molecules of different gases under the same conditions occupy the same volume.

3) under normal conditions, one mole of any gas occupies a volume of 22.4 dm3 3 (l). This volume is called molargas volume(V о) (normal conditions - t о = 0 ° С or

T about = 273 K, P about = 101325 Pa = 101.325 kPa = 760 mm. rt. Art. = 1 atm).

4) one mole of any substance and an atom of any element, regardless of the conditions and state of aggregation, contains the same number of molecules. This Avogadro's number (Avogadro's constant) - it has been experimentally established that this number is equal to

N A = 6,02213∙10 23 (molecules).

In this way: for gases 1 mol - 22.4 dm 3 (l) - 6.023 ∙ 10 23 molecules - M, g / mol ;

for substance 1 mol - 6.023 ∙ 10 23 molecules - M, g / mol.

Based on Avogadro's law: at the same pressure and the same temperatures, the masses (m) of equal volumes of gases are referred to as their molar masses (M)

m 1 / m 2 = M 1 / M 2 = D,

where D is the relative density of the first gas over the second.

According to R. Boyle's law - E. Mariotte , at constant temperature, the pressure produced by a given mass of gas is inversely proportional to the volume of gas

P about / P 1 = V 1 / V about or PV = const.

This means that as the pressure increases, the volume of the gas decreases. This law was first formulated in 1662 by R. Boyle. Since the French scientist E. Marriott was also involved in its creation, in other countries, except England, this law is called a double name. He is a special case ideal gas law(describing a hypothetical gas, ideally obeying all the laws of gas behavior).

By the law of J. Gay-Lussac : at constant pressure, the gas volume changes in direct proportion to the absolute temperature (T)

V 1 / T 1 = V o / T o or V / T = const.

The relationship between gas volume, pressure and temperature can be expressed by a general equation that combines the Boyle-Mariotte and Gay-Lussac laws ( combined gas law)

PV / T = P about V about / T about,

where P and V are the pressure and volume of the gas at a given temperature T; P about and V about - pressure and volume of gas under normal conditions (n.o.).

Mendeleev-Clapeyron equation (ideal gas equation of state) establishes the ratio of mass (m, kg), temperature (T, K), pressure (P, Pa) and volume (V, m 3) of a gas with its molar mass (M, kg / mol)

where R is the universal gas constant equal to 8,314 J / (mol K). In addition, the gas constant has two more meanings: P - mm Hg, V - cm 3 (ml), R = 62400 ;

P - atm, V - dm 3 (l), R = 0,082 .

Partial pressure (lat. partialis- partial, from lat. pars- part) is the pressure of a single component of the gas mixture. The total pressure of the gas mixture is the sum of the partial pressures of its components.

The partial pressure of a gas dissolved in a liquid is the partial pressure of the gas that would be formed in the gassing phase in a state of equilibrium with the liquid at the same temperature. The partial pressure of a gas is measured as the thermodynamic activity of gas molecules. Gases will always flow from an area of high partial pressure to an area of lower pressure; and the larger the difference, the faster the flow will be. Gases dissolve, diffuse and react according to their partial pressure and are not necessarily dependent on the concentration in the gas mixture. The law of addition of partial pressures was formulated in 1801 by J. Dalton. Moreover, the correct theoretical substantiation based on the molecular kinetic theory was made much later. Dalton's laws - two physical laws that determine the total pressure and solubility of a mixture of gases and were formulated by him at the beginning of the 19th century.

The masses of atoms and molecules are very small, so it is convenient to choose the mass of one of the atoms as a unit of measurement and express the masses of the remaining atoms relative to it. This is exactly what the founder of the atomic theory Dalton did, who compiled a table of atomic masses, taking the mass of a hydrogen atom as a unit.

Until 1961, in physics, 1/16 of the mass of an oxygen atom 16 O was taken as an atomic mass unit (amu abbreviated), and in chemistry - 1/16 of the average atomic mass of natural oxygen, which is a mixture of three isotopes. The chemical mass unit was 0.03% more than the physical one.

Currently, a unified measurement system is adopted in physics and chemistry. 1/12 of the mass of the 12 C carbon atom was chosen as the standard unit of atomic mass.

1 amu = 1/12 m (12 C) = 1.66057 × 10 -27 kg = 1.66057 × 10 -24 g.

Relative atomic and molecular weight of an element

DEFINITION

Element relative atomic mass (A r) is a dimensionless quantity equal to the ratio of the average mass of an atom of an element to 1/12 of the mass of an atom 12 C.

When calculating the relative atomic mass, the abundance of isotopes of elements in the earth's crust is taken into account. For example, chlorine has two isotopes 35 Сl (75.5%) and 37 Сl (24.5%). The relative atomic mass of chlorine is:

A r (Cl) = (0.755 × m (35 Cl) + 0.245 × m (37 Cl)) / (1/12 × m (12 C) = 35.5.

From the definition of the relative atomic mass, it follows that the average absolute mass of an atom is equal to the relative atomic mass multiplied by amu:

m (Cl) = 35.5 × 1.66057 × 10 -24 = 5.89 × 10 -23 g.

DEFINITION

Relative molecular weight (M r) is a dimensionless quantity equal to the ratio of the mass of a substance molecule to 1/12 of the mass of an atom 12 C.

Relative molecular weight of the molecule is equal to the sum of the relative atomic masses of the atoms that make up the molecule, for example:

M r (N 2 O) = 2 × A r (N) + A r (O) = 2 × 14.0067 + 15.9994 = 44.0128.

The absolute mass of the molecule equal to the relative molecular weight multiplied by amu.

The number of atoms and molecules in ordinary samples of substances is very large, therefore, when characterizing the amount of a substance, a special unit of measurement is used - the mole.

A mole is the amount of a substance that contains the same number of particles (molecules, atoms, ions, electrons) as there are carbon atoms in 12 g of the 12 C isotope.

The mass of one atom 12 С is equal to 12 amu, therefore the number of atoms in 12 g of the isotope 12 С is equal to:

N A = 12 g / 12 x 1.66057 x 10 -24 g = 1 / 1.66057 x 10 -24 = 6.0221 x 10 -23.

Thus, a mole of a substance contains 6.0221 × 10 -23 particles of this substance.

The physical quantity N A is called Avogadro's constant, it has a dimension = mol -1. The number 6.0221 × 10 -23 is called Avogadro's number.

Molar mass of matter

DEFINITION

Molar mass (M) is the mass of 1 mole of a substance.

It is easy to show that the numerical values of the molar mass M and the relative molecular mass M r are equal, but the first quantity has the dimension [M] = g / mol, and the second is dimensionless:

M = N A × m (1 molecule) = N A × M r × 1 amu = (N A × 1 amu) × M r = × M r.

This means that if the mass of a certain molecule is, for example, 44 amu, then the mass of one mole of molecules is 44 g.

Avogadro's constant is a coefficient of proportionality that ensures the transition from molecular to molar relations.

Many experiments show that molecule size very small. The linear size of a molecule or atom can be found in various ways. For example, using an electron microscope, photographs of some large molecules are obtained, and using an ion projector (ion microscope), one can not only study the structure of crystals, but determine the distance between individual atoms in a molecule.

Using the achievements of modern experimental technology, it was possible to determine the linear dimensions of simple atoms and molecules, which are about 10-8 cm. The linear dimensions of complex atoms and molecules are much larger. For example, the size of a protein molecule is 43 * 10 -8 cm.

To characterize atoms, the concept of atomic radii is used, which makes it possible to approximate the interatomic distances in molecules, liquids or solids, since atoms in their sizes do not have clear boundaries. That is atomic radius- this is the sphere, which contains the main part of the electron density of the atom (not less than 90 ... 95%).

The size of the molecule is so small that it can only be represented by comparisons. For example, a water molecule is as many times smaller than a large apple, as many times as the apple is smaller than the globe.

Mole of substance

The masses of individual molecules and atoms are very small, therefore, in calculations it is more convenient to use not absolute values of masses, but relative ones.

Relative molecular weight(or relative atomic mass) of a substance M r is the ratio of the mass of a molecule (or atom) of a given substance to 1/12 of the mass of a carbon atom.

M r = (m 0): (m 0C / 12)

where m 0 is the mass of a molecule (or atom) of a given substance, m 0C is the mass of a carbon atom.

The relative molecular (or atomic) mass of a substance shows how many times the mass of a substance molecule is more than 1/12 of the mass of the carbon isotope C 12. Relative molecular (atomic) mass is expressed in atomic mass units.

Atomic mass unit Is 1/12 of the mass of the carbon isotope C 12. Precise measurements showed that the atomic mass unit is 1.660 * 10 -27 kg, that is

1 amu = 1.660 * 10 -27 kg

The relative molecular weight of a substance can be calculated by adding the relative atomic masses of the elements that make up the substance molecule. The relative atomic mass of chemical elements is indicated in the periodic table of chemical elements by D.I. Mendeleev.

In the periodic system D.I. Mendeleev for each element is indicated atomic mass, which is measured in atomic mass units (amu). For example, the atomic mass of magnesium is 24.305 amu, that is, magnesium is twice as heavy as carbon, since the atomic mass of carbon is 12 amu. (this follows from the fact that 1 amu = 1/12 of the mass of the isotope of carbon, which makes up most of the carbon atom).

Why measure the mass of molecules and atoms in amu, if there are grams and kilograms? Of course, you can use these units as well, but it will be very inconvenient for recording (too many numbers will have to be used in order to write down the mass). To find the mass of an element in kilograms, you need to multiply the atomic mass of the element by 1 amu. Atomic mass is found according to the periodic table (written to the right of the letter designation of the element). For example, the weight of a magnesium atom in kilograms would be:

m 0Mg = 24.305 * 1 a.e.m. = 24.305 * 1.660 * 10 -27 = 40.3463 * 10 -27 kg

The mass of a molecule can be calculated by adding the masses of the elements that make up the molecule. For example, the mass of a water molecule (H 2 O) will be equal to:

m 0H2O = 2 * m 0H + m 0O = 2 * 1.00794 + 15.9994 = 18.0153 a.e.m. = 29.905 * 10 -27 kg

Moth is equal to the amount of matter in the system, which contains as many molecules as there are atoms in 0.012 kg of carbon C 12. That is, if we have a system with some substance, and in this system there are as many molecules of this substance as there are atoms in 0.012 kg of carbon, then we can say that in this system we have 1 mole of substance.

Avogadro's constant

Amount of substanceν is equal to the ratio of the number of molecules in a given body to the number of atoms in 0.012 kg of carbon, that is, the number of molecules in 1 mole of a substance.

ν = N / N A

where N is the number of molecules in a given body, N A is the number of molecules in 1 mole of the substance of which the body is composed.

N A is Avogadro's constant. The amount of a substance is measured in moles.

Avogadro's constant Is the number of molecules or atoms in 1 mole of a substance. This constant was named after an Italian chemist and physicist. Amedeo Avogadro (1776 – 1856).

1 mole of any substance contains the same number of particles.

N A = 6.02 * 10 23 mol -1

Molar mass Is the mass of a substance taken in an amount of one mole:

μ = m 0 * N A

where m 0 is the mass of the molecule.

Molar mass is expressed in kilograms per mole (kg / mol = kg * mol -1).

Molar mass is related to relative molecular mass by the ratio:

μ = 10 -3 * M r [kg * mol -1]

The mass of any amount of substance m is equal to the product of the mass of one molecule m 0 by the number of molecules:

m = m 0 N = m 0 N A ν = μν

The amount of a substance is equal to the ratio of the mass of a substance to its molar mass:

ν = m / μ

The mass of one molecule of a substance can be found if the molar mass and Avogadro's constant are known:

m 0 = m / N = m / νN A = μ / N A

A more accurate determination of the mass of atoms and molecules is achieved using a mass spectrometer - a device in which a beam of charged particles is separated in space depending on their charge mass using electric and magnetic fields.

For example, let's find the molar mass of a magnesium atom. As we found out above, the mass of a magnesium atom is equal to m0Mg = 40.3463 * 10 -27 kg. Then the molar mass will be:

μ = m 0Mg * N A = 40.3463 * 10 -27 * 6.02 * 10 23 = 2.4288 * 10 -2 kg / mol

That is, one mole "fits" 2.4288 * 10 -2 kg of magnesium. Well, or about 24.28 grams.

As you can see, the molar mass (in grams) is practically equal to the atomic mass indicated for the element in the periodic table. Therefore, when the atomic mass is indicated, it is usually done like this:

The atomic mass of magnesium is 24.305 amu. (g / mol).

MOLECULAR MASS,

the sum of the masses of the atoms that make up a given molecule; expressed in atomic mass units (amu). Since 1 a. e. m. (sometimes called dalton, D) is equal to 1/12 of the mass of an atom of the nuclide 12 C and in units of mass is 1.66057. 10 -27 kg, then the multiplication of M. m. By 1.66057. 10 -27 gives abs. the mass of the molecule in kilograms. More often they use the dimensionless value M rel-relative M. m: M rel where M x -> the mass of a molecule x, expressed in the same units of mass (kg, g, or others) as D. M. m. characterizes the average mass of a molecule, taking into account the isotopic composition of all elements that form a given chemical. compound. Sometimes M. of m is determined for a mixture of decomp. in a known composition, for example. for air, the "effective" M. m can be taken equal to 29.

Abs. It is convenient to operate with molecular masses in the field of physics of subatomic processes and radiochemistry, where by measuring the energy of particles, according to the theory of relativity, their abs are determined. masses. In chemistry and chem. technology must be applied macroscopic. units of measurement of quantity of in-va. The number of any particles (molecules, atoms, electrons, or mentally allocated in-ve groups of particles, for example, pairs of ions Na + and Cl - in the crystalline lattice of NaCl), equal to Avogadro constant N A = 6.022. 10 23 is macroscopic. unit of quantity in-va-mole. Then you can write: M rel = x... N A / (D. N A), T. e. the relative M.m. is equal to the ratio of the mass of the mole of the island to N A D. If the substance consists of molecules with covalent bonds between their constituent atoms, then the value x... N A represents the molar yu m and s with this island, the units of measure are kg-mol (kilomole, kM). For in-v, not containing molecules, but consisting of atoms, ions or radicals, the form of molar mass is determined, i.e., the mass NA particles corresponding to the accepted formula of the island (however, in the USSR, in this case, too, they often speak of M. m., which is incorrect).

Previously, chemistry used the concepts of gram-molecule, gram-atom, gram-ion, now-mole of molecules, mole of atoms, mole of ions, meaning N A of molecules, atoms, ions, etc. their molar masses, expressed in grams or kilograms. Traditionally, the term "molecular (molar) weight" is used as a synonym, since the determination of mass is carried out using a balance. But, unlike the weight, depending on the geographic. coordinates, the mass is a constant parameter of the number of islands (at normal speeds of movement of particles under chemical conditions), therefore, it is more correct to say "molecular weight".

A large number of outdated terms and concepts concerning M. m. Is explained by the fact that before the era of cosmic. flights in chemistry did not attach importance to the difference between mass and weight, a cut due to the difference in the values of acceleration free. falls at the poles (9.83 m. s -2) and at the equator (9.78 m. s -2); when calculating the force of gravity (weight), an average value of 9.81 m. s -2 is usually used. In addition, the development of the concept of a molecule (as well as an atom) was associated with the study of macroscopic. number of in-islands in the processes of their chemical. (reactions) or physical. () transformations, when the theory of the structure of the island (19th century) was not developed and it was assumed that all chemical. conn. built only from atoms and molecules.

Determination methods. Historically, the first method (substantiated by the research of S. Cannizzaro and A. Avogadro) was proposed by J. Dumas in 1827 and consisted in measuring the density of gaseous substances in relation to hydrogen gas, the molar mass of which was initially taken to be 2, and after the transition to the oxygen unit of measurement molecular and atomic masses - 2.016 g. Next. stage of development of experimental. possibilities of determining M. m. consisted in the study of liquids and solutions of non-volatile and non-dissociating in-in by measuring colligative sv-in (that is, depending only on the number of dissolved particles) - osmotic. pressure (see. Osmometry), lowering the steam pressure, lowering the freezing point ( cryoscopy) and raising the boiling point ( ebulioscopy) r-ditch in comparison with a pure r-tester. In this case, the "abnormal" behavior of electrolytes was discovered.

The decrease in vapor pressure over the solution depends on the molar fraction of the dissolved substance (Raoult's law): [( p - p 0)/R] = N, where p 0 -> steam pressure of a pure p-solvent, R- steam pressure over solution, N- molar fraction of the investigated dissolved substance, N =(t x/M x)/[(t x/M x) + (m 0 / M 0)], x and M x -sotv. hinge plate (g) and M. of m. of the investigated island, m 0 and M 0 - the same for the solution. In the course of determinations, extrapolation is carried out to infinitely decomp. solution, that is, establish for solutions of the investigated island and for solutions of the known (standard) chemical. connections. In the case of cryoscopy and ebulioscopy, dependencies are used acc. Dt 3 = Ks and Dt к = Еc, where Dt 3 is a decrease in the freezing temperature of the solution, Dt to is an increase in the boiling point of the solution, TO and E- acc. cryoscopic and ebulioscopic. constants of the solution, determined by the standard dissolved substance with precisely known M. m., s-molalnaya of the investigated substance in solution ( c = M x t x. 1000 / m 0). M. m is calculated by f-lam: M x = mx K. 1000 / m 0 Dt 3 or M x = t x E. 1000 / m 0 Dt k. The methods are characterized by a sufficiently high accuracy, since there are special. (the so-called Beckmann thermometers), which make it possible to measure very small changes in temperature.

To determine M. of m, isothermal is also used. distillation of the p-solvent. In this case, a sample of the solution of the investigated island is introduced into the chamber with sat. steam p-retel (for a given t-re); the pairs of the solution are condensed, the solution increases and after equilibrium is established, it decreases again; by the change of t-ry they judge the quantity of the released heat of evaporation, edges are connected with M. of m of the dissolved substance. In the so-called. isopiestic methods carry out isothermal. distillation of a p-solvent in a closed volume, for example. in an H-shaped vessel. In one knee of the vessel is the so-called. comparison solution containing the known mass of the substance of the known M.m. (molar concentration C 1), in another solution containing the known mass of the investigated substance (molar concentration C 2 unknown). If, for example, С 1> С 2,> The p-ratel is distilled from the second knee to the first until the molar concentrations in both knees are equal. Comparing the volumes of the obtained isopies. r-ditch, count M. m. of an unknown island. To determine M. m. It is possible to measure the mass of isopies. solutions with the help of McBen's scales, to-rye are two cups suspended on springs in a closed glass vessel; the investigated solution is placed in one cup, the comparison solution is placed in the other; by changing the position of the cups determine the masses of isopies. r-ditch and, therefore, M. of m of the investigated island.

Main method for determining atomic and mol. masses of volatile substances is mass spectrometry. To study a mixture of comp. efficient use chromatography-mass spectrometry. At low peak intensity, mol. ion use effusion. attachments to mass spectrometers. Effusio-metric. the method is based on the fact that the rate of gas outflow from the chamber through the hole, the diameter of which is much less than the average free path. the run of the molecule, is inversely proportional to the square root of M. m. in-va; the outflow rate is controlled by the change in pressure in the chamber. M. m. Volatile compounds. determined also by gas chromatography with Martin gas scales. The latter measure the speed of gas movement in the channel connecting the tubes, through which the carrier gas and the gas from the chromatographic flow are flowing. columns, which allows you to determine the difference in the densities of these gases, depending on the M. m. of the investigated island.

M. of m is measured for identification by chemical. Comm., to establish the content of individual nuclides in the Comm., for example. in water used in nuclear power engineering. installations, as well as in the study and synthesis of high-molecular-weight. Comm., St. va to-rykh essentially depend on their M. m. (see. Molecular weight of polymer). The average values of M. m. Polymers are established using the methods listed above, based on colligative sv-vah diluted solutions, according to the number of double bonds ("soft" ozonolysis) or funkts. groups (by methods of functional analysis), as well as by such St.-you of their solutions, such as light scattering. Average values of mol. masses of polymers of a high degree of polymerization are determined by their rheology. characteristics.

Lit .: Rafikov S. R., Pavlova S. A., Tverdokhlebova I. I., Methods for determination of molecular weights and polydispersity of high-molecular compounds, M., 1963; Pauling L., Pauling P., Chemistry, trans. from English., M., 1978; Vilkov L.V., Pentin Yu.A., Physical research methods in chemistry, M., 1987. Yu. A. Klyachko.

Chemical encyclopedia. - M .: Soviet encyclopedia. Ed. I. L. Knunyants. 1988 .

See what "MOLECULAR MASS" is in other dictionaries:

The mass of a molecule, expressed in atomic mass units. In practice, the molecular mass is equal to the sum of the masses of the atoms included in it (see ATOMIC MASS). Physical encyclopedic dictionary. M .: Soviet encyclopedia. Chief editor A.M. Prokhorov. 1983 ... Physical encyclopedia

- (molecular weight) the mass of the molecule, expressed in atomic mass units. It is almost equal to the sum of the masses of all the atoms that make up the molecule. Molecular weights are used in chemical, physical and chemical engineering calculations ... Big Encyclopedic Dictionary

- (mole mass), the term was previously used to refer to RELATIVE MOLECULAR MASS ... Scientific and technical encyclopedic dictionary

Molecular weight M m- Molecular weight, M. m. * Molecular weight, M. m. * Molecular mass or M. m. the mass of a molecule that does not have its own units of measurement, therefore, the term "molecular weight" is usually used in this sense (see) ... Genetics. encyclopedic Dictionary

molecular mass- - Topics of biotechnology EN molecular mass ... Technical translator's guide

Molecular mass- is the relative value, the ratio of the mass of a molecule of a given substance to 1/12 of the mass of an atom of the Carbon isotope C12. [Usherov Marshak A. V. Concrete science: lexicon. M .: RIF Building materials. 2009. - 112 p.] Term heading: General terms ... ... Encyclopedia of terms, definitions and explanations of building materials

molecular mass- santykinė molekulinė masė statusas T sritis Standartizacija ir metrologija apibrėžtis Molekulės vidutinės masės arba tiksliai apibrėžto medžiagos darinio masės ir nuklido ¹²C at maso mės 1/12 dalies dalies. atitikmenys: angl. molecular mass; ... ...

molecular mass- santykinė molekulinė masė statusas T sritis Standartizacija ir metrologija apibrėžtis Molekulę sudarančių atomų santykinių atominių masių suma, skaitine verte lygi medžiagos molio masei. atitikmenys: angl. molecular mass; molecular weight; ... ... Penkiakalbis aiškinamasis metrologijos terminų žodynas

molecular mass- santykinė molekulinė masė statusas T sritis chemija apibrėžtis Molekulę sudarančių atomų santykinių atominių masių suma, skaitine verte lygi vieno medžiagos molio masei. atitikmenys: angl. molecular mass; molecular weight; relative molecular mass ... Chemijos terminų aiškinamasis žodynas

- (molecular weight), the mass of a molecule, expressed in atomic mass units. It is almost equal to the sum of the masses of all the atoms that make up the molecule. Molecular weights are used in chemical, physical and chemical engineering calculations. * ... encyclopedic Dictionary

Books

Characteristics of hydrocarbons. Analysis of numerical data and their recommended values. Reference publication, Yu. A. Lebedev, AN Kizin, TS Papina, I. Sh. Sayfullin, Yu. E. Moshkin, This book presents the most important numerical characteristics of a number of hydrocarbons, among which the following physicochemical constants: molecular weight, temperature ... Category: Chemistry Publisher: LENAND, Manufacturer:

However, one should clearly understand the difference between molar mass and molecular mass, realizing that they are equal only numerically and differ in dimension.

The molecular masses of complex molecules can be determined simply by adding up the relative atomic masses of their constituent elements. For example, the molecular weight of water (H 2 O) is

M H 2 O = 2 Ar H + Ar O ≈ 21 + 16 = 18 amu. eat.