Molar mass of gas Calculator

The molecular masses of gas mean the sum of the atomic weights of all the atoms in a molecule. It is also called as formula weight. Molecular Weight, weight of a molecule of a substance is expressed in atomic mass units (amu). The molecular weight may be calculated from the molecular formula of the substance; it is the sum of the atomic weights of the atoms making up the molecule. Molecular weights of substances may be determined experimentally in various ways, the method employed usually depending on the state (solid, liquid, or gas) of the substance. Methods for determining the molecular weights of gaseous substances are based on Avogadro's law, which states that under given conditions of temperature and pressure a given volume of any gas contains a specific number of molecules of the gas; thus a comparison of the weights of equal volumes of different gases under the same conditions of temperature and pressure is equivalent to a direct comparison of the weights of molecules of the gases.
Molar Mass of Gas
Volume of gas (V): cm3
Mass of Gas (M): g
Temperature (T): Celcius
Pressure of gas (P): am
Molar mass of gas = :
Formula
Molar Mass of a Gas = (V * 0.0821 * (G / T) * P)

Where,
V = Volume
G = Mass of Gas
T = Temperature
P = Pressure

In order to explain how gases behave we can make the following assumptions:
  • A gas is composed of particles in constant motion.
  • The average kinetic energy depends on temperature, the higher the temperature, the higher the kinetic energy and the faster the particles are moving.
  • Compared to the space through which they travel, the particles that make up the gas are so small that their volume can be ignored.
  • The individual particles are neither attracted to one another nor do they repel one another.
  • When particles collide with one another (or the walls of the container) they bounce rather than stick. These collisions are elastic; if one particle gains kinetic energy another loses kinetic energy so that the average remains constant.

Example:
Calculate the molar mass of gas.
Enter the volume of gas = 25 cm3
Enter the mass of gas = 5 g
Enter the temperature = 10 Celcius
Enter the pressure of gas = 15 atm

Solution:
Apply Formula:
Molar Mass of a Gas = (V * 0.0821 * (G / T) * P)

Molar mass of gas: 0.0684166666