Ideal Gas Law and its Applications

Please make sure you know these concepts before proceeding: 

• Intermolecular Forces

• Combined Gas Law

When the knowledge of early observations about gases were put together, along with the proposal of the kinetic molecular theory, the idea of ideal gases was born. 

This is the equation for the ideal gas law: 

PV = nRT

• P: Pressure of Gas (atm or Torr/mmHg) 

• V: Volume of Gas (L)

• n: Moles of Gas

• R: Gas Constant

  • atm: 0.0821 L·atm/mol·K 

  • Torr: 62.3637 L·Torr/mol·K 

• T: Temperature of Gas (K)

Unit used for pressure (P) must match with the unit for the gas constant (R). 

Characteristics of (Real) Gases

• Gaseous substances can "expand" to fill any container by increasing the distance between particles. 

• Gases are lower in density than solids and liquids. 

• Gases can be compressed. 

• Gaseous particles are able to move with relatively-little resistance across space. 

• Gases can be diffused. 

• Energy transfer during particle collisions can result in a decrease of speed and therefore a decrease in temperature. 

How are Ideal Gases Different? 

According to the kinetic molecular theory: 

• Ideal gases have NO intermolecular forces. 

  • In reality, the kinetic energy of gaseous particles largely override the forces of intermolecular attraction, but miniscule dispersion forces and polarity still remain and can affect particle speed. 

• Ideal gas particles have negligible volume. 

  • Real gas particles take up dimensional space and therefore have volume. Kinetic energy is tied with mass and speed: 

    • Smaller particles with the same kinetic energy as larger particles have more speed. Also, particles with stronger intermolecular forces have slower molecular speed than particles of the same kinetic energy with less intermolecular forces. 

• Ideal gas particles don't lose kinetic energy when colliding. (Collisions are elastic.) 

As you could see, ideal gases do not match the characteristics of real gases.