Kinetic Molecular Theory - Printable Handout

Breaking Down the Name

Kinetic From the Greek kinētikos (moving). This tells us that the theory relates to motion.

Molecular From the Latin moles (mass) with a diminutive suffix. It literally means a "tiny mass" or particle.

Theory From the Greek theōria (viewing). In science, it is a highly-tested explanation of how nature works.

Put together, the Kinetic Molecular Theory (KMT) is the well-tested scientific explanation that all matter is made of tiny particles (masses) that are always in motion.

The Core Idea: States of Matter

The way particles move determines whether a substance is a solid, liquid, or gas. The hotter the substance, the faster the particles move!

Solid: Vibrate in place. Liquid: Slide past each other. Gas: Bounce around rapidly.

The 4 Parts of the KMT

1

Everything is made of particles.

2

The particles are always moving.

3

There are spaces between the particles.

4

Energy makes particles move faster and further apart.

Reading in Context: Why Do Balloons Shrink in the Cold?

Have you ever taken a helium balloon outside on a freezing winter day, only to watch it shrivel up? Did the helium escape? No!

The Kinetic Molecular Theory explains this perfectly. Inside the warm house, the gas particles are hot, meaning they have a lot of energy and are moving very fast. They constantly crash hard against the inside of the balloon, pushing the rubber outward and keeping it inflated.

When you step into the cold, the particles lose energy. According to part 4 of the KMT, lower energy means the particles slow down and take up less space. Because they are moving slower, they don't hit the inside of the balloon as hard or as often. With less outward pressure, the rubber balloon shrinks down. Bring it back inside, and as the particles heat up and speed up, the balloon will re-inflate!