How is the mass of a substance indicated? Calculations using chemical reaction equations

Let's talk about what is the amount of a substance, how this term is used in natural science subjects. Since quantitative relationships in chemistry and physics are given serious attention, it is important to know the physical meaning of all quantities, their units of measurement, and areas of application.

Designation, definition, units of measurement

In chemistry special meaning have quantitative relationships. To carry out calculations using equations, special quantities are used. In order to understand what an amount of substance is in chemistry, let’s give the term a definition. which characterizes the number of similar structural units (atoms, ions, molecules, electrons) present in a substance. To understand what the amount of a substance is, we note that this quantity has its own designation. When carrying out calculations that involve the use of this value, use the letter n. Units of measurement - mole, kmol, mmol.

Value value

Eighth-graders who do not yet know how to write chemical equations do not know what an amount of a substance is or how to use this quantity in calculations. After becoming acquainted with the law of constancy of the mass of substances, the meaning of this quantity becomes clear. For example, in the combustion reaction of hydrogen in oxygen, the ratio of reactants is two to one. If the mass of hydrogen that entered the process is known, it is possible to determine the amount of oxygen that took part in the chemical reaction.

The use of formulas for the amount of a substance allows you to reduce the ratio between the initial reagents and simplify calculations. What is the amount of a substance in chemistry? In mathematical terms, these are the stereochemical coefficients put into the equation. They are used to carry out certain calculations. Since it is inconvenient to count the number of molecules, they use Mole. Using, you can calculate that 1 mol of any reagent includes 6 1023 mol −1.

Computations

Do you want to understand what the amount of a substance is? This quantity is also used in physics. It is needed where calculations of pressure and volume of gaseous substances are carried out according to the Mendeleev-Clapeyron equation. To perform any quantitative calculations, the concept is used

By it we mean the mass that corresponds to one mole of a specific chemical substance. The molar mass can be determined through (their sum, taking into account the number of atoms in the molecule) or determined through the known mass of the substance, its quantity (mol).

Not a single problem in a school chemistry course related to calculations using an equation is complete without the use of such a term as “amount of substance.” Having mastered the algorithm, you can cope not only with ordinary software calculations, but also with complex Olympiad tasks. In addition to calculations through the mass of a substance, it is also possible using this concept, carry out calculations through molar volume. This is relevant in cases where gaseous substances take part in the interaction.

Quantity of substance used to measure macroscopic quantities of substances in many natural sciences such as physics, chemistry, in the study of electrolysis, in thermodynamics, which describes the state ideal gas. Since molecules interact regardless of their mass in quantities that are multiples of integers, when describing chemical reactions, It is more convenient to use quantities of a substance than mass. In order to understand what quantities of a substance are in chemistry, we note that a quantity has its own unit of measurement.

Definition, units of measurement, designation

The number of similar structural units contained in a substance (atoms, electrons, molecules, ions and other particles) is physical quantity- amount of substance. By international system units (SI) measure the amount of substance in [mol],[kmol],[mmol], when used in calculations, is denoted as (en).

Application, meaning

In chemistry, when writing chemical equations, after becoming familiar with the law of constancy of mass of substances, it becomes clear how to use the quantity of a substance and its meaning. For example, in the combustion reaction of hydrogen, it is required 2 to 1 the value of oxygen. Knowing the mass of hydrogen, it is possible to obtain the amount of oxygen involved in the combustion reaction.

In real experiments, instead of the quantity of a substance “in pieces”, a unit of measurement is used [mol]. This reduces the ratio of starting reagents and simplifies calculations. In fact, in 1 mole the number of units of substance contained is 6 1023 mol −1, which is called N A ].

To calculate the amount of a substance based on its mass, use the concept molar mass , i.e. the ratio of the mass of a substance to the number of moles of this substance:

n = m/M,

where m is the mass of the substance, M is the molar mass of the substance.

Molar mass measured in [g/mol].

Also molar mass can be found by work molecular weight of this substance per number of molecules in 1 mole -

Amount of gaseous substance determined based on its volume:

n = V / V m,

where where V is the volume of gas at normal conditions, A V m - molar volume gas under the same conditions, equal 22.4 l/mol according to Avogadro's law.

Summarizing all the calculations, we can deduce general formula for the amount of substance:

Computations

To more accurately understand what the amount of a substance is, let’s solve the simplest problems: what amount of substance is contained in an aluminum casting, weighing m = 5.4 kg?

When solving this problem, it should be remembered that the molar mass is numerically equal to the relative molecular mass, to find which you will need the periodic table, rounding the values: μ = 2.7 ⋅ 10-2 kg/mol.

Thus, we find the amount of substance by simple calculations:

n = m/μ = 5.4 kg/ 2.7 ⋅ 10-2 kg/mol = 2⋅ 10-2 mol.

This quantity is also used in physics. She is needed in molecular physics, where pressure and volume of gaseous substances are calculated using the Mendeleev-Clapeyron equation:

Units of measurement SI

Application

This physical quantity is used to measure macroscopic quantities of substances in cases where, for a numerical description of the processes being studied, it is necessary to take into account the microscopic structure of the substance, for example, in chemistry, when studying electrolysis processes, or in thermodynamics, when describing the equations of state of an ideal gas.

When describing chemical reactions, quantity of a substance is a more convenient quantity than mass, since molecules interact regardless of their mass in quantities that are multiples of whole numbers.

For example, the combustion reaction of hydrogen (2H 2 + O 2 → 2H 2 O) requires twice more hydrogen substances than oxygen. In this case, the mass of hydrogen participating in the reaction is approximately 8 times less than the mass of oxygen (since the atomic mass of hydrogen is approximately 16 times less atomic mass oxygen). Thus, using the quantity of a substance makes it easier to interpret reaction equations: the relationship between the quantities of reacting substances is directly reflected by the coefficients in the equations.

Since it is inconvenient to use the number of molecules directly in calculations, because this number in real experiments is too large, instead of measuring the number of molecules “in pieces,” they are measured in moles. The actual number of units of a substance in 1 mole is called Avogadro’s number (N A = 6.022 141 79(30) 10 23 mol −1) (more correctly - Avogadro's constant, since, unlike a number, this quantity has units of measurement).

The amount of a substance is denoted by the Latin n (en) and is not recommended to be denoted by the Greek letter (nu), since in chemical thermodynamics this letter denotes the stoichiometric coefficient of the substance in the reaction, and it, by definition, is positive for the reaction products and negative for the reactants. However, in school course it is widely used greek letter(nude).

To calculate the amount of a substance based on its mass, use the concept of molar mass: where m is the mass of the substance, M is the molar mass of the substance. Molar mass is the mass per mole of a given substance. The molar mass of a substance can be obtained by multiplying the molecular mass of this substance by the number of molecules in 1 mole - by Avogadro's number. Molar mass (measured in g/mol) is numerically the same as relative molecular mass.

According to Avogadro's law, the amount of a gaseous substance can also be determined based on its volume: = V / V m, where V is the volume of gas (under normal conditions), V m is the molar volume of gas at N.U., equal to 22.4 l /mol.

Thus, a valid formula combines basic calculations with the amount of substance:

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See what “Amount of substance” is in other dictionaries:

amount of substance- medžiagos kiekis statusas T sritis Standartizacija ir metrologija apibrėžtis Dydis, išreiškiamas medžiagos masės ir jos molio masės dalmeniu. atitikmenys: engl. amount of substance vok. Molmenge, f; Stoffmenge, f rus. amount of substance, n;… … Penkiakalbis aiškinamasis metrologijos terminų žodynas

amount of substance- medžiagos kiekis statusas T sritis fizika atitikmenys: engl. amount of substance vok. Stoffmenge, f rus. amount of substance, n pranc. quantité de matière, f … Fizikos terminų žodynas

Phys. a value determined by the number of structural elements (atoms, molecules, ions and other particles or their groups) contained in a substance (see Mole) ... Big Encyclopedic Polytechnic Dictionary

amount of substance retained in the body- rus content (c) of a harmful substance in the body, amount (c) of a substance retained in the body eng body burden fra charge (f) corporelle deu inkorporierte Noxe (f) spa carga (f) corporal ... Occupational safety and health. Translation into English, French, German, Spanish

small amount (of substance)- very small amount of substance - Topics oil and gas industry Synonyms very small amount of substance EN trace ... Technical Translator's Guide

Minimum quantity a substance simultaneously in production that defines the boundary between technological processes and technological processes with increased fire hazard.

Units of measurement SI

Application

For example, the combustion reaction of hydrogen (2H 2 + O 2 → 2H 2 O) requires twice as much hydrogen as oxygen. In this case, the mass of hydrogen participating in the reaction is approximately 8 times less than the mass of oxygen (since the atomic mass of hydrogen is approximately 16 times less than the atomic mass of oxygen). Thus, using the quantity of a substance makes it easier to interpret reaction equations: the relationship between the quantities of reacting substances is directly reflected by the coefficients in the equations.

The amount of a substance is denoted by the Latin n (en) and is not recommended to be denoted by the Greek letter (nu), since in chemical thermodynamics this letter denotes the stoichiometric coefficient of the substance in the reaction, and it, by definition, is positive for the reaction products and negative for the reactants. However, it is the Greek letter (nu) that is widely used in the school curriculum.

Thus, a valid formula combines basic calculations with the amount of substance:

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See what “Amount of substance” is in other dictionaries:

QUANTITY OF SUBSTANCE- physical a value determined by the number of structural elements (atoms, molecules, ions and other particles or their groups) contained in a substance (see Mole) ... Big Encyclopedic Polytechnic Dictionary

small amount (of substance)- very small amount of substance - Topics oil and gas industry Synonyms very small amount of substance EN trace ... Technical Translator's Guide

Threshold amount of substance- The minimum amount of a substance in production at a time, which determines the boundary between technological processes and technological processes of increased fire hazard.

DEFINITION

Quantity of substance is the number of structural elements (atoms, molecules, ions, etc.) in the system. The unit of measurement for the quantity of a substance is mole.

Mole- the amount of substance of the system that contains as many specific structural units (molecules, atoms, ions, electrons, etc.) as are contained in 0.012 kg of carbon-12.

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

N A = 12 g / 12 × 1.66057 × 10 -24 g = 1/1.66057 × 10 -24 = 6.0221 × 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 the dimension = mol -1. The number 6.0221×10 -23 is called Avogadro's number. Thus, the amount of substance will be calculated as:

where N is the number of structural links, and N A is Avogadro’s constant.

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, however, 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 proportionality coefficient that provides a transition from molecular to molar relationships. Therefore, another formula for calculating the amount of substance is as follows:

where m is the mass of the substance (g), and M is its molar mass (g/mol).

The amount of gas substance can be calculated using Avogadro's law: V equal volumes Different gases under the same conditions (temperature and pressure) contain the same number of molecules. Hence , under normal conditions, 1 mole of various gases occupies a volume equal to 22.4 liters. This volume is called the molar volume of the gas:

where V is the volume of gas (l), and V m is the molar volume (l/mol).