One of the basic units in the International System of Units (SI) is The unit of quantity of a substance is the mole.

Mole – this is the amount of a substance that contains as many structural units of a given substance (molecules, atoms, ions, etc.) as there are carbon atoms contained in 0.012 kg (12 g) of a carbon isotope 12 WITH .

Considering that the value of the absolute atomic mass for carbon is equal to m(C) = 1.99 10  26 kg, the number of carbon atoms can be calculated N A, contained in 0.012 kg of carbon.

A mole of any substance contains the same number of particles of this substance (structural units). The number of structural units contained in a substance with an amount of one mole is 6.02 10 23 and is called Avogadro's number (N A ).

For example, one mole of copper contains 6.02 10 23 copper atoms (Cu), and one mole of hydrogen (H 2) contains 6.02 10 23 hydrogen molecules.

Molar mass(M) is the mass of a substance taken in an amount of 1 mole.

Molar mass is designated by the letter M and has the dimension [g/mol]. In physics they use the unit [kg/kmol].

In the general case, the numerical value of the molar mass of a substance numerically coincides with the value of its relative molecular (relative atomic) mass.

For example, the relative molecular weight of water is:

Мr(Н 2 О) = 2Аr (Н) + Аr (O) = 2∙1 + 16 = 18 a.m.u.

The molar mass of water has the same value, but is expressed in g/mol:

M (H 2 O) = 18 g/mol.

Thus, a mole of water containing 6.02 10 23 water molecules (respectively 2 6.02 10 23 hydrogen atoms and 6.02 10 23 oxygen atoms) has a mass of 18 grams. Water, with an amount of substance of 1 mole, contains 2 moles of hydrogen atoms and one mole of oxygen atoms.

1.3.4. The relationship between the mass of a substance and its quantity

Knowing the mass of a substance and its chemical formula, and therefore the value of its molar mass, you can determine the amount of the substance and, conversely, knowing the amount of the substance, you can determine its mass. For such calculations you should use the formulas:

where ν is the amount of substance, [mol]; m– mass of the substance, [g] or [kg]; M – molar mass of the substance, [g/mol] or [kg/kmol].

For example, to find the mass of sodium sulfate (Na 2 SO 4) in an amount of 5 moles, we find:

1) the value of the relative molecular mass of Na 2 SO 4, which is the sum of the rounded values ​​of the relative atomic masses:

Мr(Na 2 SO 4) = 2Аr(Na) + Аr(S) + 4Аr(O) = 142,

2) a numerically equal value of the molar mass of the substance:

M(Na 2 SO 4) = 142 g/mol,

3) and, finally, the mass of 5 mol of sodium sulfate:

m = ν M = 5 mol · 142 g/mol = 710 g.

Answer: 710.

1.3.5. The relationship between the volume of a substance and its quantity

At normal conditions(n.s.), i.e. at pressure r , equal to 101325 Pa (760 mm Hg), and temperature T, equal to 273.15 K (0 С), one mole of different gases and vapors occupies the same volume equal to 22.4 l.

The volume occupied by 1 mole of gas or vapor at ground level is called molar volumegas and has the dimension liter per mole.

V mol = 22.4 l/mol.

Knowing the amount of gaseous substance (ν ) And molar volume value (V mol) you can calculate its volume (V) under normal conditions:

V = ν V mol,

where ν is the amount of substance [mol]; V – volume of gaseous substance [l]; V mol = 22.4 l/mol.

And, conversely, knowing the volume ( V) of a gaseous substance under normal conditions, its quantity (ν) can be calculated :

Along with mass and volume, chemical calculations often use the amount of a substance proportional to the number of structural units contained in the substance. In each case, it must be indicated which structural units (molecules, atoms, ions, etc.) are meant. The unit of quantity of a substance is the mole.

Mole is the amount of substance containing as many molecules, atoms, ions, electrons or other structural units as there are atoms in 12 g of the 12C carbon isotope.

The number of structural units contained in 1 mole of a substance (Avogadro's constant) is determined with great accuracy; in practical calculations it is taken equal to 6.02 1024 mol -1.

It is easy to show that the mass of 1 mole of a substance (molar mass), expressed in grams, is numerically equal to the relative molecular weight of this substance.

Thus, the relative molecular weight (or, for short, molecular weight) of free chlorine C1g is 70.90. Therefore, the molar mass of molecular chlorine is 70.90 g/mol. However, the molar mass of chlorine atoms is half as much (45.45 g/mol), since 1 mole of Cl chlorine molecules contains 2 moles of chlorine atoms.

According to Avogadro's law, equal volumes of any gases taken at the same temperature and the same pressure contain the same number of molecules. In other words, the same number of molecules of any gas occupies the same volume under the same conditions. At the same time, 1 mole of any gas contains the same number of molecules. Consequently, under the same conditions, 1 mole of any gas occupies the same volume. This volume is called the molar volume of the gas and under normal conditions (0°C, pressure 101, 425 kPa) is equal to 22.4 liters.

For example, the statement “the carbon dioxide content of the air is 0.04% (vol.)” means that at a partial pressure of CO 2 equal to the air pressure and at the same temperature, the carbon dioxide contained in the air will take up 0.04% of the total volume occupied by air.

Test task

1. Compare the number of molecules contained in 1 g of NH 4 and in 1 g of N 2. In what case and how many times is the number of molecules greater?

2. Express the mass of one sulfur dioxide molecule in grams.

4. How many molecules are there in 5.00 ml of chlorine under normal conditions?

4. What volume under normal conditions is occupied by 27 10 21 gas molecules?

5. Express the mass of one NO 2 molecule in grams -

6. What is the ratio of the volumes occupied by 1 mole of O2 and 1 mole of Oz (the conditions are the same)?

7. Equal masses of oxygen, hydrogen and methane are taken under the same conditions. Find the ratio of the volumes of gases taken.

8. To the question of how much volume 1 mole of water will occupy under normal conditions, the answer was: 22.4 liters. Is this the correct answer?

9. Express the mass of one HCl molecule in grams.

How many molecules of carbon dioxide are there in 1 liter of air if the volumetric content of CO 2 is 0.04% (normal conditions)?

10. How many moles are contained in 1 m 4 of any gas under normal conditions?

11. Express in grams the mass of one molecule of H 2 O-

12. How many moles of oxygen are in 1 liter of air, if the volume

14. How many moles of nitrogen are in 1 liter of air if its volumetric content is 78% (normal conditions)?

14. Equal masses of oxygen, hydrogen and nitrogen are taken under the same conditions. Find the ratio of the volumes of gases taken.

15. Compare the number of molecules contained in 1 g of NO 2 and in 1 g of N 2. In what case and how many times is the number of molecules greater?

16. How many molecules are contained in 2.00 ml of hydrogen under standard conditions?

17. Express in grams the mass of one molecule of H 2 O-

18. What volume under normal conditions is occupied by 17 10 21 gas molecules?

RATE OF CHEMICAL REACTIONS

When defining the concept speed chemical reaction it is necessary to distinguish between homogeneous and heterogeneous reactions. If a reaction occurs in a homogeneous system, for example, in a solution or in a mixture of gases, then it occurs throughout the entire volume of the system. Speed ​​of homogeneous reaction is the amount of a substance that reacts or is formed as a result of a reaction per unit time per unit volume of the system. Since the ratio of the number of moles of a substance to the volume in which it is distributed is the molar concentration of the substance, the rate of a homogeneous reaction can also be defined as change in concentration per unit time of any of the substances: the initial reagent or the reaction product. To ensure that the calculation result is always positive, regardless of whether it is based on a reagent or a product, the “±” sign is used in the formula:

Depending on the nature of the reaction, time can be expressed not only in seconds, as required by the SI system, but also in minutes or hours. During the reaction, the magnitude of its speed is not constant, but continuously changes: it decreases, as the concentrations of the starting substances decrease. The above calculation gives the average value of the reaction rate over a certain time interval Δτ = τ 2 – τ 1. True (instantaneous) speed is defined as the limit to which the ratio Δ tends WITH/ Δτ at Δτ → 0, i.e., the true speed is equal to the derivative of the concentration with respect to time.

For a reaction whose equation contains stoichiometric coefficients that differ from unity, the rate values ​​expressed in terms of different substances, are not the same. For example, for the reaction A + 4B = D + 2E, the consumption of substance A is one mole, that of substance B is three moles, and the supply of substance E is two moles. That's why υ (A) = ⅓ υ (B) = υ (D) =½ υ (E) or υ (E) . = ⅔ υ (IN) .

If a reaction occurs between substances located in different phases of a heterogeneous system, then it can only occur at the interface between these phases. For example, the interaction between an acid solution and a piece of metal occurs only on the surface of the metal. Speed ​​of heterogeneous reaction is the amount of a substance that reacts or is formed as a result of a reaction per unit time per unit interface surface:

.

The dependence of the rate of a chemical reaction on the concentration of reactants is expressed by the law of mass action: at a constant temperature, the rate of a chemical reaction is directly proportional to the product of the molar concentrations of the reacting substances raised to powers equal to the coefficients in the formulas of these substances in the reaction equation. Then for the reaction

2A + B → products

the ratio is valid υ ~ · WITH A 2 · WITH B, and to transition to equality a proportionality coefficient is introduced k, called reaction rate constant:

υ = k· WITH A 2 · WITH B = k·[A] 2 ·[B]

(molar concentrations in formulas can be designated as a letter WITH with the corresponding index and the formula of the substance enclosed in square brackets). Physical meaning reaction rate constants – reaction rate at concentrations of all reactants equal to 1 mol/l. The dimension of the reaction rate constant depends on the number of factors on the right side of the equation and can be c –1 ; s –1 ·(l/mol); s –1 · (l 2 /mol 2), etc., that is, such that in any case, in calculations, the reaction rate is expressed in mol · l –1 · s –1.

For heterogeneous reactions, the equation of the law of mass action includes the concentrations of only those substances that are in the gas phase or in solution. The concentration of a substance in the solid phase is a constant value and is included in the rate constant, for example, for the combustion process of coal C + O 2 = CO 2, the law of mass action is written:

υ = k I·const··= k·,

Where k= k I const.

In systems where one or more substances are gases, the rate of reaction also depends on pressure. For example, when hydrogen interacts with iodine vapor H 2 + I 2 = 2HI, the rate of the chemical reaction will be determined by the expression:

υ = k··.

If you increase the pressure, for example, by 4 times, then the volume occupied by the system will decrease by the same amount, and, consequently, the concentrations of each of the reacting substances will increase by the same amount. The reaction rate in this case will increase 9 times

Dependence of reaction rate on temperature described by van't Hoff's rule: with every 10 degree increase in temperature, the reaction rate increases by 2-4 times. This means that as the temperature rises in arithmetic progression the rate of a chemical reaction increases in geometric progression. The base in the progression formula is temperature coefficient of reaction rateγ, showing how many times the rate of a given reaction increases (or, which is the same thing, the rate constant) with an increase in temperature by 10 degrees. Mathematically, Van't Hoff's rule is expressed by the formulas:

or

where and are the reaction rates, respectively, at the initial t 1 and final t 2 temperatures. Van't Hoff's rule can also be expressed by the following relations:

; ; ; ,

where and are, respectively, the rate and rate constant of the reaction at temperature t; and – the same values ​​at temperature t +10n; n– number of “ten-degree” intervals ( n =(t 2 –t 1)/10), by which the temperature has changed (can be an integer or fractional number, positive or negative).

Test task

1. Find the value of the rate constant for the reaction A + B -> AB, if at concentrations of substances A and B equal to 0.05 and 0.01 mol/l, respectively, the reaction rate is 5 10 -5 mol/(l-min).

2. How many times will the rate of reaction 2A + B -> A2B change if the concentration of substance A is increased by 2 times, and the concentration of substance B is decreased by 2 times?

4. How many times should the concentration of the substance, B 2 in the system 2A 2 (g) + B 2 (g) = 2A 2 B (g), be increased so that when the concentration of substance A decreases by 4 times, the rate of the direct reaction does not change ?

4. Some time after the start of the reaction 3A+B->2C+D, the concentrations of substances were: [A] =0.04 mol/l; [B] = 0.01 mol/l; [C] =0.008 mol/l. What are the initial concentrations of substances A and B?

5. In the system CO + C1 2 = COC1 2, the concentration was increased from 0.04 to 0.12 mol/l, and the chlorine concentration was increased from 0.02 to 0.06 mol/l. How many times did the rate of the forward reaction increase?

6. The reaction between substances A and B is expressed by the equation: A + 2B → C. The initial concentrations are: [A] 0 = 0.04 mol/l, [B] o = 0.05 mol/l. The reaction rate constant is 0.4. Find initial speed reactions and the reaction rate after some time, when the concentration of substance A decreases by 0.01 mol/l.

7. How will the rate of the reaction 2CO + O2 = 2CO2, occurring in a closed vessel, change if the pressure is doubled?

8. Calculate how many times the reaction rate will increase if the temperature of the system is increased from 20 °C to 100 °C, taking the value temperature coefficient reaction speed equal to 4.

9. How will the reaction rate 2NO(r.) + 0 2 (g.) → 2N02(r.) change if the pressure in the system is increased by 4 times;

10. How will the reaction rate 2NO(r.) + 0 2 (g.) → 2N02(r.) change if the volume of the system is reduced by 4 times?

11. How will the rate of the reaction 2NO(r.) + 0 2 (g.) → 2N02(r.) change if the concentration of NO is increased by 4 times?

12. What is the temperature coefficient of the reaction rate if, with an increase in temperature by 40 degrees, the reaction rate

increases by 15.6 times?

14. . Find the value of the rate constant for the reaction A + B -> AB, if at concentrations of substances A and B equal to 0.07 and 0.09 mol/l, respectively, the reaction rate is 2.7 10 -5 mol/(l-min).

14. The reaction between substances A and B is expressed by the equation: A + 2B → C. The initial concentrations are: [A] 0 = 0.01 mol/l, [B] o = 0.04 mol/l. The reaction rate constant is 0.5. Find the initial reaction rate and the reaction rate after some time, when the concentration of substance A decreases by 0.01 mol/l.

15. How will the reaction rate 2NO(r.) + 0 2 (g.) → 2N02(r.) change if the pressure in the system is doubled;

16. In the system CO + C1 2 = COC1 2, the concentration was increased from 0.05 to 0.1 mol/l, and the chlorine concentration was increased from 0.04 to 0.06 mol/l. How many times did the rate of the forward reaction increase?

17. Calculate how many times the reaction rate will increase if the temperature of the system is increased from 20 °C to 80 °C, taking the value of the temperature coefficient of the reaction rate equal to 2.

18. Calculate how many times the reaction rate will increase if the temperature of the system is increased from 40 °C to 90 °C, taking the value of the temperature coefficient of the reaction rate equal to 4.

CHEMICAL BOND. FORMATION AND STRUCTURE OF MOLECULES

1.What types of chemical bonds do you know? Give an example of the formation of an ionic bond using the valence bond method.

2. Which one chemical bond called covalent? What is characteristic of covalent type connections?

4. What properties are characterized by a covalent bond? Show this with specific examples.

4. What type of chemical bond is in H2 molecules; Cl 2 HC1?

5.What is the nature of the bonds in molecules? NCI 4 CS 2, CO 2? Indicate for each of them the direction of displacement of the common electron pair.

6. What chemical bond is called ionic? What is characteristic of the ionic type of bond?

7. What type of bond is in the NaCl, N 2, Cl 2 molecules?

8. Picture everything possible ways overlap of the s-orbital with the p-orbital;. Indicate the direction of communication in this case.

9. Explain the donor-acceptor mechanism covalent bond using the example of the formation of phosphonium ion [PH 4 ]+.

10. In CO molecules, C0 2, is the bond polar or nonpolar? Explain. Describe hydrogen bonding.

11. Why are some molecules that have polar bonds generally nonpolar?

12.Covalent or ionic type of bond is typical for the following compounds: Nal, S0 2, KF? Why is an ionic bond an extreme case of a covalent bond?

14. What is metal connection? How is it different from a covalent bond? What properties of metals does it determine?

14. What is the nature of the bonds between atoms in molecules; KHF 2, H 2 0, HNO ?

15. How to explain high strength bonds between atoms in the nitrogen molecule N2 and significantly less in the phosphorus molecule P4?

16. What kind of bond is called a hydrogen bond? Why do molecules of H2S and HC1, in contrast to H2O and HF, form hydrogen bonds not typical?

17. What bond is called ionic? Does an ionic bond have the properties of saturation and directionality? Why is it an extreme case of covalent bonding?

18. What type of bond is in the molecules NaCl, N 2, Cl 2?

The mass of 1 mole of a substance is called molar. What is the volume of 1 mole of a substance called? Obviously, this is also called molar volume.

What is the molar volume of water? When we measured 1 mole of water, we did not weigh 18 g of water on the scales - this is inconvenient. We used measuring utensils: a cylinder or a beaker, since we knew that the density of water is 1 g/ml. Therefore, the molar volume of water is 18 ml/mol. For liquids and solids, the molar volume depends on their density (Fig. 52, a). It's a different matter for gases (Fig. 52, b).

Rice. 52.
Molar volumes (n.s.):
a - liquids and solids; b - gaseous substances

If you take 1 mole of hydrogen H2 (2 g), 1 mole of oxygen O2 (32 g), 1 mole of ozone O3 (48 g), 1 mole of carbon dioxide CO2 (44 g) and even 1 mole of water vapor H2 O (18 g) under the same conditions, for example normal (in chemistry it is customary to call normal conditions (n.s.) a temperature of 0 ° C and a pressure of 760 mm Hg, or 101.3 kPa), then it turns out that 1 mol of any of the gases will occupy the same volume, equal to 22.4 liters, and contain the same number of molecules - 6 × 10 23.

And if you take 44.8 liters of gas, then how much of its substance will be taken? Of course, 2 moles, since the given volume is twice the molar volume. Hence:

where V is the volume of gas. From here

Molar volume is physical quantity, equal to the ratio of the volume of a substance to the amount of a substance.

The molar volume of gaseous substances is expressed in l/mol. Vm - 22.4 l/mol. The volume of one kilomole is called kilomolar and is measured in m 3 /kmol (Vm = 22.4 m 3 /kmol). Accordingly, the millimolar volume is 22.4 ml/mmol.

Problem 1. Find the mass of 33.6 m 3 of ammonia NH 3 (n.s.).

Problem 2. Find the mass and volume (n.v.) of 18 × 10 20 molecules of hydrogen sulfide H 2 S.

When solving the problem, let's pay attention to the number of molecules 18 × 10 20. Since 10 20 is 1000 times less than 10 23, obviously, calculations should be carried out using mmol, ml/mmol and mg/mmol.

Key words and phrases

1. Molar, millimolar and kilomolar volumes of gases.
2. The molar volume of gases (under normal conditions) is 22.4 l/mol.
3. Normal conditions.

Working with a computer

1. Refer to the electronic application. Study the lesson material and complete the assigned tasks.
2. Search on the Internet email addresses, which can serve as additional sources revealing the content of keywords and phrases in the paragraph. Offer your help to the teacher in preparing a new lesson - make a report on the key words and phrases of the next paragraph.

Questions and tasks

1. Find the mass and number of molecules at n. u. for: a) 11.2 liters of oxygen; b) 5.6 m 3 nitrogen; c) 22.4 ml of chlorine.
2. Find the volume that at n. u. will take: a) 3 g of hydrogen; b) 96 kg of ozone; c) 12 × 10 20 nitrogen molecules.
3. Find the densities (mass 1 liter) of argon, chlorine, oxygen and ozone at room temperature. u. How many molecules of each substance will be contained in 1 liter under the same conditions?
4. Calculate the mass of 5 liters (n.s.): a) oxygen; b) ozone; c) carbon dioxide CO 2.
5. Indicate which is heavier: a) 5 l sulfur dioxide(SO 2) or 5 liters of carbon dioxide (CO 2); b) 2 liters of carbon dioxide (CO 2) or 3 liters of carbon monoxide (CO).

From the provisions that one mole of any substance includes the number of particles of this substance equal to Avogadro’s number, and that equal numbers particles of different gases under the same physical conditions are contained in equal volumes of these gases, the following follows:

equal quantities of any gaseous substances under the same physical conditions occupy equal volumes

For example, the volume of one mole of any gas has (at p, T = const) the same value. Consequently, the equation for a reaction occurring with the participation of gases specifies not only the ratio of their quantities and masses, but also their volumes.

molar volume of a gas (V M) is the volume of gas that contains 1 mole of particles of this gas
V M = V / n

The SI unit of molar volume of a gas is cubic meter per mole (m 3 /mol), but more often used submultiples- liter (cubic decimeter) per mole (l/mol, dm 3 /mol) and milliliter (cubic centimeter) per mole (cm 3 /mol).
In accordance with the definition of molar volume for any gas, the ratio of its volume V to quantity n will be the same provided that it is an ideal gas.

Under normal conditions (norm) - 101.3 kPa, 0°C - the molar volume of an ideal gas is equal to

V M = 2.241381·10 -2 m 3 /mol ≈ 22.4 l/mol

In chemical calculations, the rounded value of 22.4 L/mol is used because the exact value refers to ideal gas, and the majority real gases differ in properties from it. Real gases with a very low equilibrium condensation temperature (H 2, O 2, N 2) under normal conditions have a volume almost equal to 22.4 l/mol, and gases condensing at high temperatures, have a slightly lower molar volume at normal conditions: for CO 2 - 22.26 l/mol, for NH 3 - 22.08 l/mol.

Knowing the volume of a certain gas under given conditions, you can determine the amount of substances in this volume, and vice versa, by the amount of substance in a given portion of gas you can find the volume of this portion:

n = V / V M ; V = V M * n

Molar volume of gas at N.S. is a fundamental physical constant that is widely used in chemical calculations. It allows you to use the volume of gas instead of its mass, which is very convenient in analytical chemistry(gas analyzers based on volume measurement), since it is easier to measure the volume of a gas than its mass.

The value of the molar volume of gas at no. is the proportionality coefficient between the Avogadro and Loschmidt constants:

V M = N A / N L = 6.022 10 23 (mol -1) / 2.24 10 4 (cm 3 /mol) = 2.69 10 19 (cm -3)

Using the molar volume and molar mass of the gas, the density of the gas can be determined:

ρ = M / V M

In calculations based on the law of equivalents for gaseous substances (reagents, products), instead of the equivalent mass, it is more convenient to use the equivalent volume, which is the ratio of the volume of a portion of a given gas to the equivalent amount of a substance in this portion:

V eq = V / n eq = V / zn = V M / z; (p, T = const)

The equivalent volume unit is the same as the molar volume unit. The value of the equivalent volume of gas is a constant of a given gas only in a specific reaction, since it depends on the equivalence factor f eq.

Molar volume of gas

Molar volume of a gas From the provisions that one mole of any substance includes a number of particles of this substance equal to Avogadro’s number, and that equal numbers of particles of different gases at the same

Gas volume under normal conditions

Topic 1

LESSON 7

Subject. Molar volume of gases. Calculation of gas volume under normal conditions

Lesson objectives: to familiarize students with the concept of “molar volume”; reveal the features of using the concept of “molar volume” for gaseous substances; teach students to use the acquired knowledge to calculate the volume of gases under normal conditions.

Lesson type: combined.

Forms of work: teacher's story, guided practice.

Equipment: Periodic table chemical elements D. I. Mendeleev, cards with tasks, cube with a volume of 22.4 l (with a side of 28.2 cm).

II. Examination homework, updating basic knowledge

Students submit their homework completed on the sheets for verification.

1) What is “amount of substance”?

2) A unit of measurement for the amount of a substance.

3) How many particles are contained in 1 mole of a substance?

4) What is the relationship between the amount of substance and state of aggregation, in which this substance is located?

5) How many water molecules are contained in 1 mole of ice?

6) What about 1 mole of liquid water?

7) In 1 mole of water vapor?

8) What mass will they have:

III. Learning new material

Creation and solution problematic situation Problematic question. What volume will it occupy:

We cannot answer these questions right away, because the volume of a substance depends on the density of the substance. And according to the formula V = m / ρ, the volume will be different. 1 mole of steam occupies more volume than 1 mole of water or ice.

Because in liquid and gaseous substances the distance between water molecules is different.

Many scientists have studied gaseous substances. Significant contributions to the study of this issue were made by the French chemist Joseph Louis Gay-Lussac and the English physicist Robert Boyle, who formulated a number of physical laws describing the state of gases.

Of these patterns do you know?

All gases are equally compressed and have the same thermal expansion coefficient. The volumes of gases depend not on the size of individual molecules, but on the distance between molecules. The distances between molecules depend on their speed of movement, energy and, accordingly, temperature.

Based on these laws and his research, the Italian scientist Amedeo Avogadro formulated the law:

Equal volumes of different gases contain the same number of molecules.

Under normal conditions, gaseous substances have a molecular structure. Gas molecules are very small compared to the distance between them. Therefore, the volume of a gas is determined not by the size of particles (molecules), but by the distance between them, which is approximately the same for any gas.

A. Avogadro concluded that if we take 1 mole, i.e. 6.02 x 1023 molecules of any gases, they will occupy the same volume. But at the same time, this volume is measured under the same conditions, that is, at the same temperature and pressure.

The conditions under which such calculations are carried out are called normal conditions.

Normal conditions (n.v.):

T = 273 K or t = 0 °C

P = 101.3 kPa or P = 1 atm. = 760 mm Hg. Art.

The volume of 1 mole of a substance is called molar volume (Vm). For gases under normal conditions it is 22.4 l/mol.

A cube with a volume of 22.4 liters is demonstrated.

Such a cube contains 6.02-1023 molecules of any gases, for example, oxygen, hydrogen, ammonia (NH 3), methane (CH4).

Under what conditions?

At a temperature of 0 ° C and a pressure of 760 mm Hg. Art.

From Avogadro's law it follows that

where Vm = 22.4 l/mol of any gas at n. V.

So, knowing the volume of a gas, you can calculate the amount of a substance, and vice versa.

IV. Formation of skills and abilities

Practice with examples

Calculate how much volume 3 moles of oxygen will occupy at N. V.

Calculate the number of carbon(IV) oxide molecules in a volume of 44.8 liters (n.v.).

2) Calculate the number of C O 2 molecules using the formulas:

N (CO 2) = 2 mol · 6.02 · 1023 molecules/mol = 12.04 · 1023 molecules.

Answer: 12.04 · 1023 molecules.

Calculate the volume occupied by nitrogen weighing 112 g (at present).

V (N 2) = 4 mol · 22.4 l/mol = 89.6 l.

V. Homework

Work through the corresponding paragraph of the textbook and answer the questions.

Creative task (home practice). Solve problems 2, 4, 6 from the map independently.

Card task for lesson 7

Calculate how much volume 7 moles of nitrogen N2 will occupy (based on current).

Calculate the number of hydrogen molecules in a volume of 112 liters.

(Answer: 30.1 1023 molecules)

Calculate the volume of hydrogen sulfide weighing 340 g.

Gas volume under normal conditions

Molar volume of gases. Calculation of the volume of gas under normal conditions - QUANTITY OF SUBSTANCE. CALCULATIONS BY CHEMICAL FORMULAS – ALL CHEMISTRY LESSONS – 8th grade – lesson notes – chemistry lessons – Lesson plan – Lesson notes – Lesson plans – chemistry lesson developments – CHEMISTRY – Standard and academic level school curriculum– all chemistry lessons for the eighth grade of a 12-year school

Gas laws. Avogadro's law. Molar volume of gas

French scientist J.L. Gay-Lussac laid down the law volumetric relations:

For example, 1 liter of chlorine connects with 1 liter of hydrogen , forming 2 liters of hydrogen chloride ; 2 l sulfur oxide (IV) connect with 1 liter of oxygen, forming 1 liter of sulfur oxide (VI).

This law allowed the Italian scientist A. Avogadro assume that molecules of simple gases ( hydrogen, oxygen, nitrogen, chlorine, etc. ) consist of two identical atoms . When hydrogen combines with chlorine, their molecules break down into atoms, and the latter form hydrogen chloride molecules. But since two molecules of hydrogen chloride are formed from one molecule of hydrogen and one molecule of chlorine, the volume of the latter must be equal to the sum of the volumes of the original gases.
Thus, volumetric relations are easily explained if we proceed from the idea of ​​​​the diatomic nature of molecules of simple gases ( H2, Cl2, O2, N2, etc. ) - This, in turn, serves as proof of the diatomic nature of the molecules of these substances.
The study of the properties of gases allowed A. Avogadro to put forward a hypothesis, which was subsequently confirmed by experimental data, and therefore became known as Avogadro’s law:

Avogadro's law implies an important consequence: under the same conditions, 1 mole of any gas occupies the same volume.

This volume can be calculated if the mass is known 1 l gas. Under normal conditions, (n.s.) i.e. temperature 273К (О°С) and pressure 101,325 Pa (760 mmHg) , the mass of 1 liter of hydrogen is 0.09 g, molar mass its equal to 1.008 2 = 2.016 g/mol. Then the volume occupied by 1 mole of hydrogen under normal conditions is equal to 22.4 l

Under the same conditions the mass 1l oxygen 1.492g ; molar 32g/mol . Then the volume of oxygen at (n.s.) is also equal to 22.4 mol.

The molar volume of a gas is the ratio of the volume of a substance to the amount of that substance:

Where V m - molar volume of gas (dimension l/mol ); V is the volume of the system substance; n - the amount of substance in the system. Example entry: V m gas (Well.) =22.4 l/mol.

Based on Avogadro's law, the molar masses of gaseous substances are determined. The greater the mass of gas molecules, the greater the mass of the same volume of gas. Equal volumes of gases under the same conditions contain the same number of molecules, and therefore moles of gases. The ratio of the masses of equal volumes of gases is equal to the ratio of their molar masses:

Where m 1 - mass of a certain volume of the first gas; m 2 - mass of the same volume of the second gas; M 1 And M 2 - molar masses of the first and second gases.

Usually the density of a gas is determined relative to the light gas- hydrogen (denoted D H2 ). The molar mass of hydrogen is 2g/mol . Therefore we get.

The molecular mass of a substance in the gaseous state is equal to twice its hydrogen density.

Often the density of a gas is determined relative to air (D B ) . Although air is a mixture of gases, they still talk about its average molar mass. It is equal to 29 g/mol. In this case, the molar mass is determined by the expression M = 29D B .

Determination of molecular masses showed that molecules of simple gases consist of two atoms (H2, F2,Cl2, O2 N2) , and the molecules inert gases- from one atom (He, Ne, Ar, Kr, Xe, Rn). For noble gases, “molecule” and “atom” are equivalent.

Boyle-Mariotte Law: at a constant temperature, the volume of a given amount of gas is inversely proportional to the pressure under which it is located.From here pV = const ,
Where r - pressure, V - volume of gas.

Gay-Lussac's Law: at constant pressure and the change in gas volume is directly proportional to temperature, i.e.
V/T = const,
Where T - temperature on the scale TO (kelvin)

Combined gas law of Boyle - Mariotte and Gay-Lussac:
pV/T = const.
This formula is usually used to calculate the volume of a gas under given conditions if its volume under other conditions is known. If a transition is made from normal conditions (or to normal conditions), then this formula is written as follows:
pV/T = p V /T ,
Where r ,V ,T -pressure, gas volume and temperature under normal conditions ( r = 101 325 Pa , T = 273 K V =22.4 l/mol) .

If the mass and quantity of a gas are known, but it is necessary to calculate its volume, or vice versa, use Mendeleev-Clayperon equation:

Where n - amount of gas substance, mol; m - mass, g; M - molar mass of gas, g/iol ; R - universal gas constant. R = 8.31 J/(mol*K)

Gas laws

Gas laws. Avogadro's law. Molar volume of gas French scientist J.L. Gay-Lussac established the law of volumetric relations: For example, 1 liter of chlorine combines with 1 liter of hydrogen, forming 2

Amount of substance. Molar mass. Molar volume of gas. Avogadro's law
From the physics course we know about such physical quantities as mass, volume and density. Using these quantities it is easy to characterize substances. For example, we go to the store and buy 1 kg of sugar or a liter bottle of mineral water. But it turns out that these quantities are not enough if it is necessary to consider a substance from the point of view of the number of particles. How many sugar molecules are there in 1 kg of sugar? How many water molecules are in a liter bottle? And in one drop? The answer to this question can be obtained if you know about another physical quantity, which is called the amount of matter. It is difficult to calculate the exact number of molecules, but if you count not in pieces, but in portions, then the task becomes simpler. For example, we never buy matches individually in a store, but having bought one box of matches, we know that there are 100 pieces. We also don’t buy napkins individually, but having bought a pack of napkins, that is, a portion, we will know exactly how many pieces of napkins we bought.
A quantity of a substance is a portion of a substance with a certain number of structural particles. The amount of substance is usually denoted Greek letterν [nude]. In the SI system, the unit for measuring the amount of a substance is called the mole. One mole of a substance contains the same number of structural particles as there are atoms in 12 g of carbon, namely 6 * 1023 particles. This quantity is a constant value and is called “Avogadro’s constant”. The amount of a substance can be defined as the ratio of the number of structural particles to the number of particles in one mole of the substance.
For example, the amount of substance that corresponds to 3*1023 iron atoms can be easily calculated using this formula.
By transforming the original formula it is easy to determine the number of structural particles from a known amount of substance: N = v * NA
This constant received its name in honor of Amedeo Avogadro, who in 1811 made an assumption, which was then confirmed experimentally and now bears the name Avogadro's Law. Avogadro's law: “equal volumes of different gases under the same conditions (temperature and pressure) contain the same number of molecules.”
From Avogadro's law it follows that under the same conditions, masses of gases containing the same number of structural particles will occupy the same volume. At a pressure of 1 atmosphere and a temperature of 0 degrees Celsius, 1 mole of any gas occupies a volume equal to 22.4 liters. This volume is called molar volume. And the conditions are normal conditions. The molar volume is denoted by Vm and shows the volume of a gas with an amount of 1 mole. Under normal conditions it is a constant value.
Under normal conditions, the amount of a substance is the ratio of volume to molar volume.
Using this formula, you can determine the volume of a substance if its quantity is known: V = ν * Vm
The mass of a substance in an amount of 1 mole is called molar mass, denoted by the letter M. Molar mass is numerically equal to the relative molecular mass. The unit of molar mass is g/mol.
Knowing the mass of a substance, it is easy to determine the amount of the substance.

Let's find the amount of substance 5.6 g of iron.
To find the mass of a substance from a known quantity, we transform the formula: m = ν * M
Reference material
The quantity of a substance ν [nu] is a physical quantity that characterizes the number of structural units of the same type (any particles that make up a substance - atoms, molecules, ions, etc.) contained in a substance. The unit of measurement for the quantity of a substance in the International System of Units (SI) is the mole.
A mole is a unit of measurement for the amount of a substance. One mole of a substance contains the same number of structural particles as there are atoms in 12 g of carbon.
Molar mass (M) is the mass of a substance in an amount of one mole. Unit g/mol.
Normal conditions (n.s.) – physical conditions defined by a pressure of 101325 Pa (normal atmosphere) and a temperature of 273.15 K (0 °C).
Molar volume (Vm) is the volume of a substance of one mole. Unit of measurement: l/mol; at no. Vm = 22.4 l/mol
Avogadro's law - equal volumes of different gases under the same conditions (temperature and pressure) contain the same number of molecules.
Avogadro's constant (NA) shows the number of structural particles in a substance of one mole.