Moles are units of measurements that are used frequently in Physics and Chemistry. One mole of contains  6.02214179 × 10^23 atoms. The number 6.02214179 × 10^23 is called Avogadro's number or Avogadro's constant, which is represented by “NA”. This was discovered by the scientist Amedeo Avogadro. The mole is preferred because it can be used to represent a great number of molecules, atoms or any substance. 

Standard Temperature and Pressure. The standard temperature is 273 K, 0° Celsius or 32° Fahrenheit, and the standard pressure is 1 atm pressure. 

A unit of temperature commonly used in Physics, this scale was discovered by an Scottish scientist, William Thomson. 

The pascal is a unit that is used to measure pressure or stress. The pascal was named after a scientist named, Blaise Pascal.
Gas: A gas is a state of matter that consist of particles do not have any shape or volume. 

 The force that applied on a surface by the air above it as gravity pulls it to Earth, is defined as the Atmospheric pressure. In simpler terms, in can be defined as the pressure that the world around us naturally has. 

Internal energy is the total potential energy of s system and s system's kinetic energy. the particles in an ideal gas are considered to be point objects that have elastic collisions with each other.

This is 1.38064852 × 10-23 m2 kg s-2 K-1, this is a constant relates the kinetic energy of particles in a gas with the temperature of the gas. 

Elastic collision is a collision where there is no loss in kinetic energy in a system as a result of the collision.