What Is Avogadro's Law?

Avogadro's law (Avogadro's Hypothesis) (English name: Avogadro's Hypothesis) mainly explains: at the same temperature and pressure, any gas of the same volume contains the same number of molecules, called Avogadro law. The volume of gas refers to the space occupied by the molecules. Under normal conditions, the average distance between gas molecules is about 10 times the molecular diameter. Therefore, when the number of molecules contained in a gas is determined, the volume of the gas is mainly determined by the intermolecular The average distance, not the size of the molecule itself. ^[1]

Avogadro's law (Avogadro's Hypothesis) (English name: Avogadro's Hypothesis) mainly explains: at the same temperature and pressure, any gas of the same volume contains the same number of molecules, called Avogadro law. The volume of gas refers to the space occupied by the molecules. Under normal conditions, the average distance between gas molecules is about 10 times the molecular diameter. Therefore, when the number of molecules contained in a gas is determined, the volume of the gas is mainly determined by the intermolecular The average distance, not the size of the molecule itself. ^[1]

Chinese name

Avogadro's Law

Foreign name

Avogadro's Hypothesis

nickname

Four Laws

Presenter

Avogadro

Applied discipline

Physics, Chemistry

Scope of application

Thermal

Scope of application

Molecular theory

Definition of Avogadro's Law

At the same temperature and pressure, any gas of the same volume contains the same number of molecules. Therefore, it is also called the Four Laws of Law, also called the Five Laws of Law, or the Kelaberon equation (five same refers to the same temperature, the same pressure, the same volume, the same number of molecules, and the same amount of material).

Scope of Avogadro's Law

Ideal gas (that is, gas has no volume and no interaction between molecules. PS: At high temperature and pressure, many gases are close to ideal gas), it can be a single gas or a mixed gas. It may be a simple substance gas or a compound gas.

Inference of Avogadro's Law

Avogadro's Law

(1) At the same temperature and pressure,

(Gas volume ratio is equal to the ratio of the amount of substance)

(2) At the same temperature and volume,

(Pressure ratio equals the ratio of the amount of substance equal to the ratio of the number of molecules)

(3) At the same temperature and pressure,

(4) At the same temperature and pressure, M1 / M2 = P1 / P2

_{(The ratio of the molar mass of the gas is equal to the ratio of the density)}

The average distance between molecules depends on the outside temperature and pressure. When the temperature and pressure are the same, the average distance between any gas molecules is almost equal (the interaction between gas molecules is weak and can be ignored), so the law holds. This law is widely used in chemical reactions involving gas, inferring the molecular formula of unknown gas, and so on.

Avogadro's law states that at the same temperature and pressure, the same volume of gas contains the same number of molecules. The hypothesis was proposed by Italian chemist Avogadro in 1811, and was later recognized by the scientific community. This law reveals the volume relationship of gas reactions, which is used to explain the composition of gas molecules, and provides a basis for measuring the molecular weight of gaseous substances by gas density method. The establishment of the atomic molecule theory also played a certain positive role.

Avogadro's Law Equation

The Clapeyron equation is also called the "ideal gas equation". In secondary school chemistry, Avogadro's law occupies a very important position. It is widely used, especially when calculating the molecular formula and molecular weight of gaseous substances. If the method is used, it is very convenient to solve the problem. The following introduces several relations derived from the Clabron equation to better understand and use Avogadro's law.

Clapeyron equation is usually expressed by the following formula: PV = nRT

P is a pressure, V is a gas volume, n is a substance amount, T is an absolute temperature, and R is a gas constant. The R values are the same for all gases. If pressure, temperature and volume are in SI, R = 8.31 Pa · m 3 / mol · K. If the pressure is atmospheric pressure and the volume is liter, R = 0.082 atmosphere · liter / mole · degree.

Because n = m / M, = m / v (nthe amount of matter, mthe mass of matter, Mthe molar mass of matter, numerically equal to the molecular weight of the matter, and the density of the gaseous matter), The dragon equation can also be written in the following two forms:

Pv = mRT / M and PM = RT

The discussion is based on A and B gases.

(1) When the same T, P, V:

According to the formula: nA = nB (ie Avogadro's law)

Certain molecular weight

Molar mass ratio = density ratio = relative density. If mA = mB then MA = MB.

(2) At the same T, P, and m:

The ratio of volume = inverse ratio of molar mass; the ratio of the amount of two gas substances = inverse ratio of molar mass.

The ratio of the amount of substance = the inverse ratio of gas density; the ratio of the volume of two gases = the inverse ratio of gas density.

(3) At the same T · V:

The ratio of the pressure of the two gases = the direct ratio of the molecular weight of the gas = the inverse ratio of the molar mass.

Corollary of Avogadro's Law

We can use Avogadro's law and the relationship between the amount of matter and the number of molecules and molar mass to get the following useful inferences:

(1) At the same temperature and pressure: V1: V2 = n1: n2 = N1: N2 1: 2 = M1: M2 Same quality: V1: V2 = M2: M1

(2) At the same temperature and volume: P1: P2 = n1: n2 = N1: N2 At the same mass: P1: P2 = M2: M1

(3) At the same temperature, same pressure and same volume: 1: 2 = M1: M2 = m1: m2

Please refer to the specific derivation process to help memorize. The reasoning process is briefly described as follows:

(1) At the same temperature and pressure, the same volume of gas contains the same number of molecules, so we know that at the same temperature and pressure, the gas volume is proportional to the number of molecules, that is, proportional to the amount of their substance, That is, V = kn for any gas; therefore, V1: V2 = n1: n2 = N1: N2, and then n = m / M has formula ; if the gas mass is the same, then formula .

(2) From Avogadro's law, it is known that when the temperature, volume, and number of gas molecules are the same, the pressure is also the same, that is, the pressure of the gas is proportional to the number of molecules at the same temperature and volume. The rest of the derivation is the same as (1).

(3) At the same temperature, same pressure and same volume, the amount of gas must be the same. According to n = m / M and = m / V, there is formula . Of course, these conclusions apply not only to two gases, but also to multiple gases.

Avogadro's Law Relative Density

At the same temperature and pressure, the density ratios appearing in the above formulae and are called the relative density of the gas D = 1: 2 = M1: M2.

Note: .D is called relative density of gas 1 relative to gas 2 and has no unit. For example, the density of oxygen to hydrogen is 16.

. If the volume is the same at the same time, it is also equal to the mass ratio, that is, D = m1: m2.

Inference of Avogadro's Law

Avogadro's law and inferences can be derived from the equation of state of ideal gas and its deformation (pressure, volume, absolute temperature, amount of matter, gas constant, density). It can be derived from the law: "One continuous ratio, three positive ratios, three inverse ratios".

1. "Continuous ratio" refers to the ratio of the mass ratio of any gas of the same volume at the same temperature and pressure to the molar mass (relative molecular mass) and equal to the density ratio.

2. "Three proportional"

(1) At the same temperature and pressure, the ratio of the volume of two gases is equal to the ratio of the amount of its substance and the ratio of its number of molecules.

(2) At the same temperature and the same volume, the ratio of the pressure of two gases is equal to the ratio of the amount of its substance and the ratio of its number of molecules.

(3) At the same temperature and pressure, the ratio of the density of two gases is equal to the ratio of their molar masses (also called relative molecular masses).

3 "Three inverse ratio"

(1) At the same temperature and pressure and mass, the volume of two gases is inversely proportional to their molar mass (relative molecular mass).

(2) At the same temperature and the same number of molecules (or the amount of equivalent substances), the pressure of the two gases is inversely proportional to their volume.

(3) At the same temperature and the same volume and the same mass (at the same density), the pressure of the two gases is inversely proportional to their molar mass (relative molecular mass).