Before solving problems, you should know the formulas and rules of how to find the volume of gas. We should remember Avogadro's law. And the volume of gas itself can be calculated using several formulas, choosing the appropriate one from them. When selecting the required formula, environmental conditions, in particular temperature and pressure, are of great importance.
Avogadro's law
It says that at the same pressure and the same temperature, the same volumes of different gases will contain the same number of molecules. The number of gas molecules contained in one mole is Avogadro's number. From this law it follows that: 1 Kmol (kilomol) of an ideal gas, any gas, at the same pressure and temperature (760 mm Hg and t = 0*C) always occupies one volume = 22.4136 m3.
How to determine gas volume
- The formula V=n*Vm can most often be found in problems. Here the volume of gas in liters is V, Vm is the molar volume of gas (l/mol), which under normal conditions = 22.4 l/mol, and n is the amount of substance in moles. When the conditions do not have the amount of a substance, but there is a mass of the substance, then we proceed this way: n=m/M. Here M is g/mol (molar mass of the substance), and the mass of the substance in grams is m. In the periodic table it is written under each element, as its atomic mass. Let's add up all the masses and get what we are looking for.
- So, how to calculate the volume of gas. Here is the task: dissolve 10 g of aluminum in hydrochloric acid. Question: how much hydrogen can be released at u.? The reaction equation looks like this: 2Al+6HCl(g)=2AlCl3+3H2. At the very beginning, we find the aluminum (quantity) that reacted according to the formula: n(Al)=m(Al)/M(Al). We take the mass of aluminum (molar) from the periodic table M(Al) = 27 g/mol. Let's substitute: n(Al)=10/27=0.37 mol. From the chemical equation it can be seen that 3 moles of hydrogen are formed when 2 moles of aluminum are dissolved. It is necessary to calculate how much hydrogen will be released from 0.4 moles of aluminum: n(H2)=3*0.37/2=0.56mol. Let's substitute the data into the formula and find the volume of this gas. V=n*Vm=0.56*22.4=12.54l.
In order to find out the composition of any gaseous substances, you must be able to operate with concepts such as molar volume, molar mass and density of the substance. In this article, we will look at what molar volume is and how to calculate it?
Quantity of substance
Quantitative calculations are carried out in order to actually carry out a particular process or to find out the composition and structure of a certain substance. These calculations are inconvenient to perform with absolute values of the mass of atoms or molecules due to the fact that they are very small. Relative atomic masses also cannot be used in most cases, since they are not related to generally accepted measures of mass or volume of a substance. Therefore, the concept of quantity of a substance was introduced, which is denoted by the Greek letter v (nu) or n. The amount of a substance is proportional to the number of structural units (molecules, atomic particles) contained in the substance.
The unit of quantity of a substance is the mole.
A mole is an amount of substance that contains the same number of structural units as there are atoms contained in 12 g of a carbon isotope.
The mass of 1 atom is 12 a. e.m., therefore the number of atoms in 12 g of carbon isotope is equal to:
Na= 12g/12*1.66057*10 to the power-24g=6.0221*10 to the power of 23
The physical quantity Na is called Avogadro's constant. One mole of any substance contains 6.02 * 10 to the power of 23 particles.
Rice. 1. Avogadro's law.
Molar volume of gas
The molar volume of a gas is the ratio of the volume of a substance to the amount of that substance. This value is calculated by dividing the molar mass of a substance by its density using the following formula:
where Vm is the molar volume, M is the molar mass, and p is the density of the substance.
Rice. 2. Molar volume formula.
In the international C system, the molar volume of gaseous substances is measured in cubic meters per mole (m 3 /mol)
The molar volume of gaseous substances differs from substances in liquid and solid states in that a gaseous element with an amount of 1 mole always occupies the same volume (if the same parameters are met).
The volume of gas depends on temperature and pressure, so when calculating, you should take the volume of gas under normal conditions. Normal conditions are considered to be a temperature of 0 degrees and a pressure of 101.325 kPa. The molar volume of 1 mole of gas under normal conditions is always the same and equal to 22.41 dm 3 /mol. This volume is called the molar volume of an ideal gas. That is, in 1 mole of any gas (oxygen, hydrogen, air) the volume is 22.41 dm 3 /m.
Rice. 3. Molar volume of gas under normal conditions.
Table "molar volume of gases"
The following table shows the volume of some gases:
| Gas | Molar volume, l |
| H 2 | 22,432 |
| O2 | 22,391 |
| Cl2 | 22,022 |
| CO2 | 22,263 |
| NH 3 | 22,065 |
| SO 2 | 21,888 |
| Ideal | 22,41383 |
The volume of 1 mole of a substance is called the Molar volume. Molar mass of 1 mole of water = 18 g/mol 18 g of water occupy a volume of 18 ml. This means the molar volume of water is 18 ml. 18 g of water occupy a volume equal to 18 ml, because the density of water is 1 g/ml CONCLUSION: Molar volume depends on the density of the substance (for liquids and solids).
1 mole of any gas under normal conditions occupies the same volume equal to 22.4 liters. Normal conditions and their designations no. (0 0 C and 760 mmHg; 1 atm.; 101.3 kPa). The volume of a gas with 1 mole of substance is called molar volume and is denoted by – V m
Solving problems Problem 1 Given: V(NH 3) n.s. = 33.6 m 3 Find: m - ? Solution: 1. Calculate the molar mass of ammonia: M(NH 3) = = 17 kg/kmol
CONCLUSIONS 1. The volume of 1 mole of a substance is called the molar volume V m 2. For liquid and solid substances, the molar volume depends on their density 3. V m = 22.4 l/mol 4. Normal conditions (n.s.): and pressure 760 mmHg, or 101.3 kPa 5. The molar volume of gaseous substances is expressed in l/mol, ml/mmol,
Names of acids are formed from the Russian name of the central atom of the acid with the addition of suffixes and endings. If the oxidation state of the central atom of the acid corresponds to the group number of the Periodic Table, then the name is formed using the simplest adjective from the name of the element: H 2 SO 4 - sulfuric acid, HMnO 4 - manganese acid. If acid-forming elements have two oxidation states, then the intermediate oxidation state is denoted by the suffix –ist-: H 2 SO 3 – sulfurous acid, HNO 2 – nitrous acid. Various suffixes are used for the names of halogen acids that have many oxidation states: typical examples are HClO 4 - chlorine n acid, HClO 3 – chlorine novat acid, HClO 2 – chlorine ist acid, HClO – chlorine novatist ic acid (oxygen-free acid HCl is called hydrochloric acid - usually hydrochloric acid). Acids can differ in the number of water molecules that hydrate the oxide. Acids containing the largest number of hydrogen atoms are called ortho acids: H 4 SiO 4 - orthosilicic acid, H 3 PO 4 - orthophosphoric acid. Acids containing 1 or 2 hydrogen atoms are called metaacids: H 2 SiO 3 - metasilicic acid, HPO 3 - metaphosphoric acid. Acids containing two central atoms are called di acids: H 2 S 2 O 7 – disulfuric acid, H 4 P 2 O 7 – diphosphoric acid.
The names of complex compounds are formed in the same way as names of salts, but the complex cation or anion is given a systematic name, that is, it is read from right to left: K 3 - potassium hexafluoroferrate(III), SO 4 - tetraammine copper(II) sulfate.
Names of oxides are formed using the word “oxide” and the genitive case of the Russian name of the central atom of the oxide, indicating, if necessary, the oxidation state of the element: Al 2 O 3 - aluminum oxide, Fe 2 O 3 - iron (III) oxide.
Names of bases are formed using the word “hydroxide” and the genitive case of the Russian name of the central hydroxide atom, indicating, if necessary, the oxidation state of the element: Al(OH) 3 - aluminum hydroxide, Fe(OH) 3 - iron(III) hydroxide.
Names of compounds with hydrogen are formed depending on the acid-base properties of these compounds. For gaseous acid-forming compounds with hydrogen, the following names are used: H 2 S – sulfane (hydrogen sulfide), H 2 Se – selan (hydrogen selenide), HI – hydrogen iodide; their solutions in water are called hydrogen sulfide, hydroselenic and hydroiodic acids, respectively. For some compounds with hydrogen, special names are used: NH 3 - ammonia, N 2 H 4 - hydrazine, PH 3 - phosphine. Compounds with hydrogen having an oxidation state of –1 are called hydrides: NaH is sodium hydride, CaH 2 is calcium hydride.
Names of salts are formed from the Latin name of the central atom of the acidic residue with the addition of prefixes and suffixes. The names of binary (two-element) salts are formed using the suffix - eid: NaCl – sodium chloride, Na 2 S – sodium sulfide. If the central atom of an oxygen-containing acidic residue has two positive oxidation states, then the highest oxidation state is denoted by the suffix – at: Na 2 SO 4 – sulf at sodium, KNO 3 – nitr at potassium, and the lowest oxidation state is the suffix - it: Na 2 SO 3 – sulf it sodium, KNO 2 – nitr it potassium To name oxygen-containing halogen salts, prefixes and suffixes are used: KClO 4 – lane chlorine at potassium, Mg(ClO 3) 2 – chlorine at magnesium, KClO 2 – chlorine it potassium, KClO – hypo chlorine it potassium
Covalent saturationsconnectionto her– manifests itself in the fact that in compounds of s- and p-elements there are no unpaired electrons, that is, all unpaired electrons of atoms form bonding electron pairs (exceptions are NO, NO 2, ClO 2 and ClO 3).
Lone electron pairs (LEP) are electrons that occupy atomic orbitals in pairs. The presence of NEP determines the ability of anions or molecules to form donor-acceptor bonds as donors of electron pairs.
Unpaired electrons are electrons of an atom, contained one in an orbital. For s- and p-elements, the number of unpaired electrons determines how many bonding electron pairs a given atom can form with other atoms through the exchange mechanism. The valence bond method assumes that the number of unpaired electrons can be increased by lone electron pairs if there are vacant orbitals within the valence electron level. In most compounds of s- and p-elements there are no unpaired electrons, since all unpaired electrons of the atoms form bonds. However, molecules with unpaired electrons exist, for example, NO, NO 2, they have increased reactivity and tend to form dimers like N 2 O 4 due to unpaired electrons.
Normal concentration – this is the number of moles equivalents in 1 liter of solution.
Normal conditions - temperature 273K (0 o C), pressure 101.3 kPa (1 atm).
Exchange and donor-acceptor mechanisms of chemical bond formation. The formation of covalent bonds between atoms can occur in two ways. If the formation of a bonding electron pair occurs due to the unpaired electrons of both bonded atoms, then this method of formation of a bonding electron pair is called an exchange mechanism - the atoms exchange electrons, and the bonding electrons belong to both bonded atoms. If the bonding electron pair is formed due to the lone electron pair of one atom and the vacant orbital of another atom, then such formation of the bonding electron pair is a donor-acceptor mechanism (see. valence bond method).
Reversible ionic reactions – these are reactions in which products are formed that are capable of forming starting substances (if we keep in mind the written equation, then about reversible reactions we can say that they can proceed in one direction or another with the formation of weak electrolytes or poorly soluble compounds). Reversible ionic reactions are often characterized by incomplete conversion; since during a reversible ionic reaction, molecules or ions are formed that cause a shift towards the initial reaction products, that is, they seem to “slow down” the reaction. Reversible ionic reactions are described using the ⇄ sign, and irreversible ones - the → sign. An example of a reversible ionic reaction is the reaction H 2 S + Fe 2+ ⇄ FeS + 2H +, and an example of an irreversible one is S 2- + Fe 2+ → FeS.
Oxidizing agents – substances in which, during redox reactions, the oxidation states of some elements decrease.
Redox duality – the ability of substances to act in redox reactions as an oxidizing or reducing agent depending on the partner (for example, H 2 O 2, NaNO 2).
Redox reactions(OVR) – These are chemical reactions during which the oxidation states of the elements of the reacting substances change.
Oxidation-reduction potential – a value characterizing the redox ability (strength) of both the oxidizing agent and the reducing agent that make up the corresponding half-reaction. Thus, the redox potential of the Cl 2 /Cl - pair, equal to 1.36 V, characterizes molecular chlorine as an oxidizing agent and chloride ion as a reducing agent.
Oxides – compounds of elements with oxygen in which oxygen has an oxidation state of –2.
Orientation interactions– intermolecular interactions of polar molecules.
Osmosis – the phenomenon of transfer of solvent molecules on a semi-permeable (permeable only to solvent) membrane towards a lower solvent concentration.
Osmotic pressure – physicochemical property of solutions due to the ability of membranes to pass only solvent molecules. Osmotic pressure from a less concentrated solution equalizes the rate of penetration of solvent molecules into both sides of the membrane. The osmotic pressure of a solution is equal to the pressure of a gas in which the concentration of molecules is the same as the concentration of particles in the solution.
Arrhenius bases – substances that split off hydroxide ions during electrolytic dissociation.
Bronsted bases - compounds (molecules or ions of the S 2-, HS - type) that can attach hydrogen ions.
Grounds according to Lewis (Lewis bases) – compounds (molecules or ions) with lone pairs of electrons capable of forming donor-acceptor bonds. The most common Lewis base is water molecules, which have strong donor properties.