Kinetic Particle Model Of Matter

A super attractive model - the kinetic kind😄

You must have learned about the states of the matter before. In this guide, we shall use the kinetic model of matter to explain ‘why’ solids, liquids, and gasses have particular properties that define their existence.

States of Matter

Matter exists in three basic states: solids, liquids, and gasses.

Here is a table demonstrating comparisons between the general properties of solids, liquids, and gases:

		Solids	Liquids	Gasses
1	Description	Fixed volume. Fixed shape.	Fixed volume. Takes the shape of its container.	Variable volume. Takes the shape of its container.
2	Arrangement of particles	Arranged in a regular pattern called a lattice.	Random.	Random.
3	Separation of particles (intermolecular gap)	Close together. Tightly packed.	A little close together Slightly further apart than in solid phase.	Separated Far apart.
4	Movement of particles	Vibration about a fixed position.	Slow movement in a random way from place to place with molecules sliding past each other.	Fast, random movement.
5	Attractive forces between particles	Stronger than in the liquid phase.	Slightly weaker than in the solid phase.	No attractive forces between the particles.

A helpful simulation

Now, it is your turn. Use the information from the table above and put it to test in the simulation below.

Here is a document with information on how to make the most of the simulation:

states-of-matter-basics-simulation-guide

Guide to the States of Matter Simulation. Credits: PHET Colorado.

states-of-matter-basics-simulation-guide.pdf

605 KB

Changes in state

grayscale photography of water drops ice — Icicles are an excellent example of liquid water changing state.

Heat a cube of ice (a solid), and it changes to a runny liquid. Continue heating, and the liquid vanishes! It sounds like a magic trick, but the real fact is that the ice cube has simply changed states!

Here is a table expressing the changes of state:

Melting	A solid to a liquid
Boiling	A liquid to a gas
Condensation	A gas to a liquid
Freezing	A liquid to a solid
Sublimation	A solid to a gas
De-sublimation	A gas to a solid

The kinetic model of matter

The kinetic model of matter is a model in which matter consists of molecules in motion.

‘Kinetic’ means ‘related to movement’ (see our guide to energy transformations for more information). In the kinetic model of matter, the things that are moving are the particles (which could be atoms, ions, and molecules), and thus, it is also known as the particle model of matter.

Properties of solids and the kinetic model of matter

Property	Reasoning
Solids have a fixed shape and do not flow	As the particles of a solid are packed closely together, they are unable to flow; however they can vibrate in their positions.
Solids cannot be compressed and retain their shape	The particles of a solid have less intermolecular space, hence t hey cannot be compressed and retain their shape.
Most solids expand when they melt	As the particles are slightly apart in a liquid

Properties of liquids and the kinetic model of matter

Property	Reasoning
Liquids take up the shape of their container.	As, their particles are free to move about within the bulk of the liquid.
Dissolved substances diffuse throughout a liquid	As the mobile particles of the liquid can move, they carry the dissolved substances. The hotter the liquid, the faster the rate of diffusion.
Liquids expand a lot when they boil	As the intermolecular space between the particles of a gas is larger than a liquid.

Properties of gasses and the kinetic model of matter

Property	Reasoning
Gases take the shape of their container	As their particles can move freely about
Gasses diffuse from one place to another	As the particles of a gas are freely mobile
Gasses contract a lot when they condense	As the intermolecular space between the particles of a liquid is lesser than a gas.

Evaporation

smoke near bridge — Evaporation is the backbone of geothermal systems

Evaporation is the change in state from a liquid to a gas at a temperature below its boiling point.

Evaporation occurs only when the particles of a liquid with the greatest energy escape from the surface of the liquid. This is the reason why the evaporation of sweat from the surface of your skin results in a decrease in your internal body temperature.

Factors affecting evaporation

Factor	Explanation
A liquid evaporates more rapidly when it is hotter.	High temperatures give the particles of the liquid energy to escape off its surface.
A liquid evaporates more rapidly when it has a greater surface area.	An increased surface area means, more particles of the liquid are near the surface, and so they can escape easily.
A liquid evaporates more rapidly when a draught blows across its surface.	Particles of the liquid nearer to its surface are blown away when a draught flows.

Common misconceptions: Often students mistake between boiling and evaporation; please be clear:

Evaporation occurs at any temperature – not just the boiling point
Evaporation only happens at the surface of the liquid – not throughout the liquid, like boiling
Boiling requires a steady energy source; evaporation doesn’t require a steady energy source.

Brownian motion

bee perched on sunflower — Observing the movement of Pollen helped drive studies of properties of liquids and gasses

Brownian motion is the motion of small particles suspended in a liquid or a gas caused by molecular bombardment.

Brownian motion is named in honor of its first investigator, Robert Brown. Brown was using a microscope to study pollen grains when he noticed tiny particles moving haphazardly.

This motion is called Brownian motion.

Brownian motion occurs because the pollen grains are bombarded constantly by the smaller, lighter particles in which they are suspended (liquid or gas). This gives us evidence of the properties of liquids and gases.

Temperature and the absolute scale in Gases

3 clear glass bottles on brown wooden shelf

As a gas's temperature rises while its volume is maintained, the molecules within the gas accumulate kinetic energy and their velocity increases.

This heightened movement leads to more frequent and forceful impacts against the walls of their container, which in turn elevates the pressure inside.

Conversely, if we compress the volume of a constant amount of gas without altering its temperature, we limit the room available for molecular motion.

The molecules, still moving at the same speed, now collide with the walls more often due to the diminished space, causing an uptick in pressure.

Boyle’s law

Boyle's law articulates that for a certain quantity of gas, an inverse relationship exists between pressure and volume when temperature remains unchanged.

As volume decreases, pressure increases proportionally so long as the temperature is constant.

The equation for this is:

\begin{array}{c} p V = c o n s t a n t \\ p_{1} V_{1} = p_{2} V_{2} = c o n s t a n t \end{array}

where = pressure and = volume
These equations are only valid if the temperature is kept constant.

Celsius and Kelvin temperature scales

The Celsius (°C) and Kelvin (K) temperature scales are two ways of measuring temperature in scientific contexts.

To convert a temperature from Celsius to Kelvin, you can use the simple formula:

[ K = °C + 273.15 ]

This equation reflects the fact that 0 degrees Celsius is equivalent to 273.15 Kelvin.

The Kelvin scale starts at absolute zero, which is the theoretical point where all molecular motion ceases, and it is set as 0 Kelvin (-273.15°C). On the other hand, to convert from Kelvin to Celsius:

[ °C = K - 273.15 ]

Yay! Finally, your revision for this chapter is complete! Woohoo! A very particular song came to my mind while I was revising. Thank me later!

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