Avogadro’s Law Formula

Avogadro’s Law: According to Avogadro’s law, the quantity of moles in a gas and its volume are directly proportional under conditions of constant pressure and temperature. Avogadro’s initial theory was this. Ideal gases were subject to this law, although real gases slightly deviate from it.

The quantity (number of moles) and volume of an ideal gas are directly proportional to each other for a given mass of the gas at constant temperature and pressure, according to the contemporary meaning of Avogadro’s law.

Avogadro’s Law Formula

The mathematical formulation of Avogadro’s law is:

V ∝ n or V/n = k

Where “V” stands for the gas’s volume, “n” for its mass (or number of moles), and “k” is a constant for a specific pressure and temperature.

Under the same pressure and temperature, equal quantities of all gases have the same number of molecules, according to Avogadro’s law. So long as the temperature and pressure are the same, identical volumes of two distinct gases will contain the same number of molecules.

Italian physicist Amadeo Avogadro was active in the 19th century. He is renowned for making significant contributions to chemistry at a time when the subject was only recently recognised as a distinct science. His work was similar to that of Robert Boyle (Boyle’s Law), Jacques Charles (Charles Law), and others. In fact, one of the laws upon which the Ideal Gas Law is based is Avogadro’s Law, the hypothesis he proposed.

The definition of an ideal gas is a gas in which the collisions between its molecules are elastic, meaning that no momentum or kinetic energy is lost, and in which the molecules have no intermolecular forces of attraction, meaning that they only interact randomly.

Let’s go over some fundamentals first, though, before we begin to comprehend his work.

A mole is a unit of measurement for the volume of a substance. A material is said to have one mole when it contains the same number of units as the number of carbon atoms in 12 grammes of C-12 carbon.

It’s also important to keep in mind that many of these laws are based on STP, or standard temperature and pressure. For STP, the temperature value is 273.15 K, or 0°C, and the pressure value is 1 atm, or 760mmHg.

Avogadro, Amedeo (Image Credit: Wikimedia Commons)

Avogadro’s number

The number of gas molecules in a mole is known as Avogadro’s number. The current value of this number is enormous—it is 6.022 x 1023. Mol-1 is the SI unit for Avogadro’s number. This indicates that the quantity in issue is measured in terms of moles. N is frequently used to represent Avogadro’s number.

It’s interesting to note that Amedeo Avogadro did not discover Avogadro’s number, unlike what is commonly believed. After Avogadro’s passing, the idea of a mole and the estimation of the significance of his number were developed. In reality, Avogadro’s number bears his name in recognition of his work and discovery.

Josef Loschmidt, an Austrian high school science teacher who later became a professor at the University of Vienna, was the first to determine the total number of particles that make up a substance.

Loschmidt calculated the number of particles in one cubic centimetre of gas at standard pressure and temperature using the kinetic molecular theory. The Loschmidt constant, which he estimated back in 1865, has a value of 2.6867773 x 1025 m-3.

The first person to use the phrase “Avogadro’s number” was a French physicist named Jean Baptiste Perrin. Using the results of his research into Brownian motion, he published an estimate of the Avogadro’s number in 1909. Brownian motion is the random, unplanned movement of small particles floating in a gas or liquid, for the uninitiated.

Only after American scientist Robert Millikan successfully measured the charge on an electron was it feasible to determine the Avogadro’s number with accuracy. Before this, it was already known how much charge there was on a mole of electrons; this charge, known as the “Faraday constant,” is equal to 96,485.3383 coulombs per mole of electrons.

To comprehend how enormous this figure is, certain comparisons have been made. One of the simplest to understand is that, if this many unpopped popcorn kernels were dispersed over the territory of the United States, when they were all popped, the popcorn would cover the continent to a depth of 9 miles (for comparison, the United States is 3.797 square miles!).

You probably noticed that I mentioned the most recent Avogadro’s number estimate. This is due to the fact that multiple approaches have been employed to calculate the value over the years since it was first established. Although the results from each method are essentially the same, there are small differences. Therefore, that is the acceptable value according to the most recent calculations. Loschmidt was the first to perform this computation, though.

Moles to Grams

The formula below can be used to convert moles to grammes, another widely used unit of measurement for amount.

grams/molar mass for moles

One must utilise the periodic table, which is always useful, to determine a substance’s molar mass. It can be computed by simply adding up each atom’s mass in the substance. If one needs to determine the molar mass of NaCl, for example

Na has a mass number of 22.99 g/mol.

Cl’s mass number is 35.45 g/mol.

NaCl’s molar mass is 22.99 + 35.45 = 58.44 g/mol as a result.

There are numerous uses for Avogadro’s number in physics and chemistry. Additionally, certain generalisations have been made. For instance, at STP, 1 mole of a gas has a volume of 22.4L. These are quite helpful for computations.

Around the world, chemists utilise Avogadro’s number. He may not have known it, but his work set the standard for these calculations.