Kinetic Particle Model Of Matter

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Notes

States of Matter

**Solids**: definite shape and volume; cannot flow; not compressible.
**Liquids**: no definite shape but definite volume; can flow; not compressible.
**Gases**: no definite shape or volume; can flow; highly compressible.
Changes of state are **physical changes** – mass and number of molecules remain constant; only energy changes.
**Melting**: solid → liquid. **Freezing**: liquid → solid.
**Boiling/evaporating**: liquid → gas. **Condensing**: gas → liquid.

Molecular Matter – Particle Arrangement & Motion

In **solids**: particles are **close together** in a **regular pattern**; they **vibrate about fixed positions**.
In **liquids**: particles are **close together** but **randomly arranged**; they **slide past each other**.
In **gases**: particles are **widely separated** (~10× further apart); they **move randomly at high speeds**.
Density: **high** in solids, **medium** in liquids, **low** in gases.
Energy: **lowest** in solids, **greater** in liquids, **highest** in gases.
**Intermolecular forces** (Extended): strong in solids (fixed shape), weaker in liquids (can flow), negligible in gases (free motion).

Particle Model of Gases

Gas particles are in **constant random motion**, colliding with each other and container walls.
**Pressure** is caused by **collisions of particles with the walls** – force per unit area: p = \frac{F}{A} .
Higher temperature → particles move **faster** → more frequent/harder collisions → **higher pressure**.
At constant temperature, **compressing** a gas (decreasing volume) **increases pressure**; **expanding** decreases pressure.
**Boyle's Law** (Extended): For fixed mass at constant temperature, p \propto \frac{1}{V} or pV = \text{constant} .

Brownian Motion

**Brownian motion**: random, erratic motion of **microscopic particles** (e.g., pollen, smoke) suspended in a fluid.
First observed by **Robert Brown** (pollen grains in water).
Caused by **collisions with smaller, fast-moving molecules** (atoms/molecules of the fluid) that are too small to see.
The visible particles change speed/direction randomly each time they are struck – evidence for the **kinetic theory of matter**.

Gases & Absolute Temperature

**Absolute zero** = **−273 °C** (0 K) – lowest possible temperature; particles have minimum kinetic energy.
**Kelvin scale**: T(\text{K}) = \θ(\degree\text{C}) + 273 , \θ(\degree\text{C}) = T(\text{K}) - 273 .
An increase of **1 K** equals an increase of **1 °C**.
At constant volume, **pressure is directly proportional to absolute temperature** (in K).
**Pressure–temperature graph** is a straight line through the origin (when temperature in K).

Gas Laws – Pressure & Volume (Extended)

**Boyle's Law**: For a fixed mass of gas at constant temperature, p₁ V₁ = p₂ V₂ .
Pressure and volume are **inversely proportional**: halving volume doubles pressure.
Graph of p vs V is a **hyperbola** (curve tending towards axes).
When gas is compressed, molecules hit walls **more often** → greater net force → higher pressure.

Particle arrangement in solids (regular, close, vibrating), liquids (close, random, sliding), and gases (far apart, random, fast motion).

Practice questions

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1.Which of the following best describes the arrangement and motion of particles in a solid?
Easy
- AParticles are close together in a regular pattern and vibrate about fixed positions.
- BParticles are close together in a random arrangement and can slide past each other.
- CParticles are far apart and move randomly at high speeds.
- DParticles are close together in a regular pattern and move freely.
2.A liquid has no definite shape but has a definite volume. Which property of liquids explains this?
Easy
- AParticles are far apart and move randomly.
- BParticles are close together but can slide past each other.
- CParticles are in fixed positions and vibrate.
- DParticles are widely separated and compressible.
3.A sealed piston is used to expand a gas at constant temperature. No gas escapes. What happens to the density and pressure of the gas?
Medium
- ADensity increases, pressure increases.
- BDensity decreases, pressure decreases.
- CDensity stays the same, pressure decreases.
- DDensity decreases, pressure stays the same.
4.Which change of state involves particles moving much closer together but continuing to travel throughout the substance?
Easy
- AMelting
- BFreezing
- CBoiling
- DCondensing
5.A sealed rigid container of fixed volume is filled with air and placed in a freezer. The temperature of the air decreases. Which row correctly describes the changes?
Medium
- AAverage distance between particles: decreases; Average speed: decreases
- BAverage distance between particles: no change; Average speed: decreases
- CAverage distance between particles: increases; Average speed: decreases
- DAverage distance between particles: no change; Average speed: increases
6.A balloon is filled with air and tied closed. It is placed in a refrigerator. As the temperature decreases, what happens to the average speed of the air molecules and the pressure inside the balloon?
Hard
- AAverage speed decreases, pressure decreases.
- BAverage speed decreases, pressure stays the same.
- CAverage speed stays the same, pressure decreases.
- DAverage speed increases, pressure decreases.
7.Brownian motion is observed when smoke particles are viewed through a microscope. What causes the smoke particles to move randomly?
Easy
- AThe smoke particles are attracted to each other.
- BThe smoke particles vibrate because they are warm.
- CSmaller air particles collide with the smoke particles.
- DThe microscope vibrates slightly.
8.A gas is heated in a closed container of constant volume. What happens to the particles of the gas?
Medium
- AThey expand.
- BThey get closer together.
- CThey hit the container walls with less force.
- DThey move faster.

Slides

States of Matter

Solids have a definite shape and volume, cannot flow, and are not compressible.
Liquids have a definite volume but no fixed shape; they flow and are not compressible.
Gases have no fixed shape or volume; they flow and are highly compressible.

Which row correctly describes the properties of a liquid?

Definite shape and volume, cannot flow
No definite shape, definite volume, can flow
No definite shape or volume, can flow
Definite shape, no definite volume, cannot flow

Changes of State

Melting: solid → liquid (e.g., ice to water).
Freezing: liquid → solid.
Boiling/Evaporating: liquid → gas.
Condensing: gas → liquid.
Changes of state are physical changes; mass remains constant, only energy changes.

When a solid turns into a liquid, the process is called ____. When a gas turns into a liquid, it is called ____.

Molecular Arrangement and Motion

Solid: particles close together in a regular pattern, vibrate about fixed positions.
Liquid: particles close together but randomly arranged, can slide past each other.
Gas: particles far apart (≈10× further in each direction), move randomly at high speeds.

Which of these are true about particles in a solid?

They vibrate about fixed positions.
They are arranged in a regular pattern.
They can slide past each other.
They are very close together.

Particle Model of Gases

Gas particles are in constant random motion at high speeds.
They collide with each other and with the walls of the container.
Pressure in a gas is caused by collisions of particles with the container walls.
Faster particles (higher temperature) cause more frequent and forceful collisions, increasing pressure.

What causes the pressure exerted by a gas on its container?

The weight of the gas particles
Collisions of gas particles with the container walls
Attraction between gas particles
The volume of the gas

Brownian Motion

Brownian motion is the random movement of microscopic particles (e.g., pollen, smoke) suspended in a fluid.
It is caused by collisions with smaller, fast-moving molecules (e.g., air or water molecules) that are too small to see.
This provides evidence for the kinetic theory of matter.

What causes smoke particles to move randomly when viewed through a microscope?

They are attracted to each other.
They vibrate because they are warm.
Smaller air particles collide with them.
The microscope vibrates.

Absolute Temperature

Absolute zero is the lowest possible temperature: 0 K = -273 °C.
At absolute zero, particles have minimum kinetic energy (stationary).
To convert: T(K) = θ(°C) + 273; θ(°C) = T(K) - 273.
An increase of 1 K equals an increase of 1 °C.

Absolute zero is ____ K, which is equal to ____ °C.

Gas Laws: Pressure and Volume (Constant Temperature)

For a fixed mass of gas at constant temperature, pressure is inversely proportional to volume: p ∝ 1/V.
Boyle's Law: pV = constant, or p₁V₁ = p₂V₂.
Compressing a gas (decreasing volume) increases pressure; expanding decreases pressure.

A gas is compressed at constant temperature. What happens to its pressure?

It increases.
It decreases.
It stays the same.
It becomes zero.

Gas Laws: Pressure and Temperature (Constant Volume)

For a fixed mass of gas at constant volume, pressure is directly proportional to absolute temperature: p ∝ T.
Increasing temperature increases average kinetic energy of particles, leading to more frequent and forceful collisions with walls, thus higher pressure.

Which statements are true about a gas heated at constant volume?

The average speed of particles increases.
The pressure decreases.
Particles collide with walls more often.
The volume of the gas increases.

Summary of Key Points

Three states of matter: solid, liquid, gas — each with distinct particle arrangement and motion.
Changes of state are physical and reversible.
Gas pressure arises from particle collisions with container walls.
Brownian motion provides evidence for particle theory.
Absolute zero is 0 K (-273 °C); Kelvin scale used in gas laws.
Boyle's Law: pV = constant at constant temperature.
At constant volume, pressure ∝ absolute temperature.

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