# What is Avogadro’s law?

## Avogadro’s Law

The **law of Avogadro** also known by the name of **Avogadro ‘s hypothesis** or the **principle** of **Avogadro** ‘s law of **gases** which indicates that under the same conditions of **pressure** and **temperature** , the **volume** equal to possess all gases contain the same amount of **molecules** . The law is named after Amedeo Avogadro who, in 1811, hypothesized that two given samples of an **ideal gas** with the same **volume** and at the same **temperature** and **pressure** contain the same**number of molecules** ; and therefore, the number of molecules or atoms in a specific volume of ideal gas is **independent** of its size or the molar mass of the gas.

Avogadro’s law or Avogadro’s hypothesis is a gas law that is responsible for establishing a **relationship** between the **volume** and the **amount** of **gas** under pressure and over the **temperatures** that are **constant** .

## What is Avogadro’s law?

Avogadro’s law states that, for a **mass** of an **ideal gas** , the **volume** of the gas and the number of **moles** are directly **proportional** if the **temperature** and **pressure** are **constant** . From the law of it can be deduced that for a given mass of an ideal gas, its **volume** and the **number** of molecules are directly **proportional as** long as the temperature and pressure are constant. The most significant **consequence** that Avogadro’s law has taught us is that the constant R for ideal gases has the**same value** for all gases.

## History

**Amadeo Avogadro** , an important **Italian physicist** , proposed in 1811 two different **hypotheses** , one of them said that the atoms of **elemental gases** were found together in molecules instead of being in **separate atoms** , as **John Dalton** had affirmed . The second hypothesis I had was that equal **volumes** of **gases at** constant **pressure** and **temperature** had the same number of molecules.

Avogadro’s hypothesis that it was related to the number of molecules that gases had was not accepted until **1858** , when the Italian chemist **Stanislao Cannizzaro** built a **logical ****system** based on the hypothesis.

## Who Proposed Avogadro’s Law

The law was first proposed in 1811 by **Amedeo Avogadro** , a senior physics professor who worked at the **University of Turin** for many years, but his theory was not well accepted until after **1858** , when an Italian chemist, **Stanislao Cannizzaro** , built a logical chemistry system based on it.

## Statement

Avogadro’s hypothesis or law can be stated as follows:

*” Equal volumes of different gases contain the same number of particles , at the same pressure and temperature “*

## Formula

**Mathematically it can be expressed with the following equation:**

**V / n = K**

V = **volume of the gas** , generally expressed in liters.

n = amount of the **substance** measured in **moles** .

Also, from the so-called ideal gas law we have the following:

**PV = nRT**

P = gas pressure is usually expressed in atmospheres (atm), in mm of mercury (mmHg) or in Pascal (Pa).

At present, we know that the **pressure** and **temperature** that are **constant** , the same amount of gas has the same volume regardless of the chemical element that forms it. The **volume** (V) is directly **proportional** to the amount of **gas ****particles** (n). Therefore the **formula of Avogadro’s law is the following** :

**V _{1} / n _{1} = V _{2} / n _{2}**

And therefore:

- If you
**increase**the amount of gas, you increase the volume. - If
**decreases**the amount of gas decreases volume.

## Experiments

Avogadro’s hypothesis can be tested as follows:

At 0ºC you have a 500.0 milliliter flask to which you can add or remove gas, a balance that measures its mass and a manometer that measures pressure. When the “tare” button is pressed, the mass of the flask will have to be deducted from the measurements.

Gas is then introduced into the flask until a certain pressure is reached; the mass of said gas must be noted. This procedure is repeated with the other gases to check that: if the volume, pressure and temperature are constant in all cases there are the same amount of particles (although the masses are different).

## Avogadro’s law applications

The gas or Avogadro law can be used to explain the **mechanics** by which **pressure** , **temperature** and **volume** are affected . For example, we can observe it in air conditioners, refrigerators and in the formation of clouds.

## Importance

Avogadro’s law has been of great importance for the world of chemistry because through it it is possible to know the **number of molecules** that are contained in a **mole** .

## Examples

Some examples of exercises already solved regarding **Avogadro’s law** are:

**Example 1: 0.5 moles of a gas occupying 2 liters. Calculate what the new volume will be if 1 mole of gas is added at constant pressure and temperatures.**

V _{1} / n _{1} = V _{2} / n _{2}

V _{1} = 2 liters

n _{1} = 0.5 moles

n _{2} = 0.5 + 1 = 1.5 moles

V _{2} = V _{1} n _{2} / n _{1} = 2 1.5 / 0.5 = 6 liters