The Basics of Kinetic Molecular Theory in Chemistry | General Chemistry 2

What is Kinetic Molecular Theory?

Kinetic Molecular Theory is a model that attempts to explain what happens in terms of groups of atoms and molecules colliding with each other and how those collisions change their energy levels, as well as their physical and chemical properties. The main points of Kinetic Molecular Theory can be summarized as:

  • Energy exists as microscopic particles called molecules.
  • Molecules have kinetic energy. 
  • The kinetic energy of molecules increases as temperature rises.
  • Gas particles are in constant motion, colliding with each other continuously.
  • When gas particles collide, they exert equal but opposite forces on each other. If the collision is perfectly elastic, then the total kinetic energy of the system remains exactly the same.
  • The average kinetic energy of a group of gas molecules depends on the temperature.
  • Atoms or groups of atoms can only absorb specific amounts of energy that are related to their individual structures.
  • The energy absorbed or released in a collision can affect the velocity of gas particles.

Kinetic energy refers to the total amount of energy possessed by molecules at a given temperature, not including any potential or gravitational energy. The Kinetic Energy of an object is dependent upon the mass and speed towards which it travels. This means that if there are more molecules, they will have more kinetic energy. This also means that if the temperature is higher, the molecules will move faster and possess greater kinetic energy.


Who Created the Theory?

In the 19th century, two great minds led humanity in understanding kinetic energy in Chemistry. James Clerk Maxwell & Ludwig Boltzmann, in collaboration with one another, established what is now known as classical thermochemistry. This theory has been an essential part of modern science ever since its inception!


What are the Main Types of Kinetic Energy?

Kinetic energy is the type of power that allows for movement. There are five major forms, including: 

  • Electrical
  • Mechanical 
  • Radiant
  • Sound
  • Thermal 

Each form has different characteristics but it's all created through kinetic motion- which can be anything from turning on a light, converting chemical energy into electricity, or knocking against something else in order to make noise.


What Happens to Kinetic Energy When a Catalyst is Added?

When two particles collide, the faster one will have more kinetic energy than the slower. Solids (bodies made from cohesive elements) have the least kinetic energy, liquids (liquids held together by surface tension) has limited potential kinetic energy, and gases (volume motion without condensation) are the most active. 

When a catalyst (such as heat) is added to a system, it usually increases the rate of particle collisions. This increase in kinetic energy can cause an endothermic (heat absorbing) or exothermic (heat releasing) reaction to occur. However, for a collision to occur in the first place, the particles must have some kinetic energy to start with. This is known as activation energy.

A good example to understand the theory is water, which can exist in all three states of matter: solid, liquid, and gas. When a catalyst is added (such as a change in temperature), it can go through the following changes in phases:

gas → liquid: condensation
gas → solid: deposition/re-sublimation
liquid → solid: freezing

liquid → gas: boiling
solid → gas: sublimation
solid → liquid: melting


What Two Factors Influence Kinetic Energy?

Mass and speed.  

The total amount of energy possessed will vary depending on how heavy the molecules are and how fast they move. A heavier molecule has more potential kinetic energy than a lighter one, and a faster-moving molecule will have greater kinetic energy than one that is slower and less massive.


How is Chemical Kinetics Used in Real Life?

In a world where so many of our most basic needs are met through technology, it is easy to take for granted how complex and intricate the human body really is. It's been said that without chemical reactions from fire or photosynthesis in plants all around us, life as we know it would not exist!

The human body is one of the best examples of how kinetic energy can be used effectively in an environment where it's needed most! When you consume food, your body breaks that down into its most basic compounds and can then either release the energy for work or convert it to stored chemicals (such as fat).