Knowing the amount of a substance in moles and Avogadro's number, it is very easy to calculate how many molecules are contained in this substance. Simply multiply Avogadro's number by the amount of substance.
N=N A *ν
And if you come to the clinic to take tests, say, blood sugar, knowing Avogadro’s number, you can easily count the number of sugar molecules in your blood. Well, for example, the analysis showed 5 mol. Let's multiply this result by Avogadro's number and get 3,010,000,000,000,000,000,000,000 pieces. Looking at this figure, it becomes clear why they stopped measuring molecules in pieces and began measuring them in moles.
Molar mass (M).
If the amount of a substance is unknown, then it can be found by dividing the mass of the substance by its molar mass.
N=N A * m / M .
The only question that may arise here is: “what is molar mass?” No, this is not a mass of painter, as it might seem!!! Molar mass is the mass of one mole of a substance. Everything is simple here, if one mole contains N A particles (i.e. equal to Avogadro's number), then, multiplying the mass of one such particle m 0 by Avogadro's number, we get the molar mass.
M=m 0 *N A .
Molar mass is the mass of one mole of a substance.
And it’s good if it’s known, but what if it’s not? We will have to calculate the mass of one molecule m 0 . But this is not a problem either. You only need to know its chemical formula and have the periodic table at hand.
Relative molecular weight (Mr).
If the number of molecules in a substance is very large, then the mass of one molecule m0, on the contrary, is very small. Therefore, for the convenience of calculations, we introduced relative molecular mass (Mr). This is the ratio of the mass of one molecule or atom of a substance to 1/12 of the mass of a carbon atom. But don’t let this scare you, for atoms it is indicated in the periodic table, and for molecules it is calculated as the sum of the relative molecular masses of all atoms included in the molecule. Relative molecular weight is measured in atomic mass units (a.u.m), in terms of kilograms 1 amu = 1.67 10 -27 kg. Knowing this, we can easily determine the mass of one molecule by multiplying the relative molecular mass by 1.67 10 -27.
m 0 = M r *1.67*10 -27 .
Relative molecular weight- the ratio of the mass of one molecule or atom of a substance to 1/12 of the mass of a carbon atom.
Relationship between molar and molecular mass.
Let us recall the formula for finding the molar mass:
M=m 0 *N A .
Because m 0 = M r * 1.67 10 -27, we can express molar mass as:
M=M r *N A *1.67 10 -27 .
Now if we multiply Avogadro's number N A by 1.67 10 -27, we get 10 -3, that is, to find out the molar mass of a substance, it is enough just to multiply its molecular mass by 10 -3.
M=M r *10 -3
But don’t rush to do all this by calculating the number of molecules. If we know the mass of a substance m, then dividing it by the mass of the molecule m 0, we get the number of molecules in this substance.
N=m / m 0
Of course, it is a thankless task to count molecules; not only are they small, they are also constantly moving. Just in case you get lost, you'll have to count again. But in science, as in the army, there is such a word “must”, and therefore even atoms and molecules were counted...
Quantity 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 consists. 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 the 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 the 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 relationship:
μ = 10 -3 * M r [kg*mol -1 ]
The mass of any quantity 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 the 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
Ideal gas - mathematical model gas, in which it is assumed that the potential interaction energy of molecules can be neglected in comparison with their kinetic energy. There are no forces of attraction or repulsion between molecules, collisions of particles with each other and with the walls of the vessel are absolutely elastic, and the interaction time between molecules is negligible compared to the average time between collisions. In the extended model of an ideal gas, the particles of which it consists also have a shape in the form of elastic spheres or ellipsoids, which makes it possible to take into account the energy of not only translational, but also rotational-vibrational motion, as well as not only central, but also non-central collisions of particles, etc. )