Empirical derivation of gas equation


Many important relationships describe the characteristics of the gas samples that have been entirely empirically derived i.e, rather than attempting to define the hypothetical reason in which these relationships might exist, it means they are only based on observations. So, these are the empirical gas laws.

There are numerous methods to derive the Empirical Ideal Gas Law, however, the easiest method is to utilize the three simplistic gas laws.

AVOGADRO’S LAW asserts that the gas volume is directly proportional to the no. of moles.

V ∝ n

BOYLE’S LAW asserts that the gas volume is inversely proportional to its pressure.

V ∝ 1/P

CHARLES’S LAW says that the gas volume

is directly proportional to its absolute temperature.

V ∝ T

In detail:

Boyle’s Law

One of the most significant relationships that rule the gas samples and which can be mathematically modeled is volume and pressure relationship. The law showcases that for a fixed gas sample at constant T, volume and pressure are inversely proportional to each other.


Or p1V2=p2V2

Charles’ Law

As per Charles’ Law, it states that a fixed gas sample volume is proportional to a temperature at constant pressure. Charles’ law works in the condition since there’s specifically the absolute minimum in the scale of volume, so there should be the absolute minimum in the scale of temperature!

VT = constant

Or, V1T2 =V1T2

Even the second law of thermodynamics estimates the absolute minimum temperature.


Gay-Lussac’s Law

With the help of Charles’ Law, it suggests that the absolute minimum exists at the scale of the temperature because pressure can never be (-ve) negative.

pT = constant

Or, p1T2 = p1T2

Combined Gas Law

When the gas laws, Charles’law, Boyle’s law, and Gay-Lussac’s Law are combined into one single empirical formula, which is useful. For the given quantity of gas, the relationship should be:



p1V1T1 = p2V2T2

Avogadro’s Law

In the statement of Avogadro’s Law, it defines that at the same pressure and temperature, any gas sample has the same molecules’ number per unit volume.


Or, n1V1 = n2V2


From empirical relationships found amongst temperature, volume, pressure, and the number of moles present in a gas, the ideal gas law is being derived. Also, it can be used in calculating any of the 4 properties if 3 out of them are known to you.

Ideal gas equation:



R=0.08206 L⋅atm/K⋅mol = 8.3145 J/K⋅mol

General gas equation: PiViniTi = PfVfnfTf

The density of a gas: ρ = MPRT

Empirical relations between temperature, volume, pressure, and the gas quantity can be joined into ideal gas law, which is PV = nRT.

R, the proportionality constant, is known as the gas constant and consist of 0.08206 (L•atm)/(K•mol), or 1.9872 cal/(K•mol), or 8.3145 J/(K•mol) value, which depends on the how units are used.

The behavior of an ideal gas is being described by the ideal gas law which is a theoretical or assumed substance whose behavior is known to be quantitatively described by gas’s Kinetic Molecular Theory and the ideal gas law. STP (Standard Temperature and Pressure) is 0-degree Celsius and 1-atm.

Ideal gas containing 1 mol of volume at Standard Temperature and Pressure of 22.4 L is the “standard molar volume.” All empirical relationships of gases are ideal gas law’s special cases, in which 2 out of 4 parameters are kept constant.

Ideal gas law allows the calculation of the fourth quantity value (P, V, T, or n), when a gaseous sample is required to be described, when you can predict the values of P, V, T, or n quantities and others are known, following conditional changes if P, V, T, and n values are known. Also, ideal gas law can be used for the calculation of the gas density only if its molar mass is known to you, or vice-versa can calculate the molar mass of a not known sample of gas if its density is calculated.


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