Chemistry For GCSE Edexcel by KANAYATI ®: 1. STATES OF MATTER GCSE EDEXCEL CHEMISTRY NOTES

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States of matter

Introduction : Kinetic particle theory

The kinetic particle theory explains the properties of the different states of matter.
The particles in solids, liquids and gases have different amounts of energy.

They are arranged differently and move in different ways.

2.1 Describe the arrangement, movement and the relative energy of particles

in each of the three states of matter: solid, liquid and gas

The three states of matter are solid, liquid and gas

They can be represented by a simple model where particles are represented
by small solid spheres

solids- particles have a regular arrangement and are close together

liquids- particles have a random arrangement and are close together

gases- particles have a random arrangement and are spread apart

Comparison Table of particle arrangement and movement in the 3 states

The table below summarizes the arrangement and movement of the particles

in solids, liquids and gases, and shows simple diagrams for the arrangement

of the particles.

Solids

The table shows some of the properties of solids and why they are like this.

Liquids

The table shows some of the properties of liquids and why they are like this.

Gases

The table shows some of the properties of gases and why they are like this.

Summary

2.2 Recall the names used for the inter conversions between the three states of matter, recognizing that these are physical changes: contrasted with chemical reactions that result in chemical changes

Melting and freezing take place at the melting point
o solid → liquid: melting
o liquid → solid: freezing

Boiling and condensing take place at the boiling point

o liquid → gas: boiling
o gas → liquid: condensing

● State changes (melting, boiling, freezing and condensing) are physical changes – they involve the forces between the particles of the substances but the particles themselves don’t change.

● Chemical changes are where a new product has been formed

2.3 Explain the changes in arrangement, movement and energy of particles during these interconversions

Particle theory can help to explain melting, boiling, freezing and condensing...

o The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the
particles of the substance.
o The nature of the particles involved depends on the type of bonding and the structure of the substance.
o The stronger the forces between the particles the higher the melting point and boiling point of the substance.

When substances are heated, the particles absorb thermal energy which is converted into kinetic energy.

Heating a solid causes its particles to vibrate more and as the temperature increases, they vibrate so much that the solid expands until the structure breaks and the solid melts.

On further heating, the now liquid substance expands more and some particles at the surface gain sufficient energy to overcome the intermolecular forces and evaporate.

When the b.p. temperature is reached, all the particles gain enough energy to escape and the liquids boils.

While changing state, the temperature of the substance remains the same as the heat energy is rapidly converted into kinetic energy. This is called latent heat.

Melting

Melting is when a solid changes into a liquid.

Requires heat energy which transforms into kinetic energy, allowing the particles to move.

Occurs at a specific temperature known as the melting point (m.p.) which is unique to each pure solid.

Boiling

Boiling is when a liquid changes into a gas.

Requires heat which causes bubbles of gas to form below the surface of a liquid, allowing for liquid particles to escape from the surface and within the liquid.

Occurs at a specific temperature known as the boiling point (b.p.) which is unique to each pure liquid.

Freezing

Freezing is when a liquid changes into a solid.

This is the reverse of melting and occurs at exactly the same temperature as melting, hence the melting point and freezing point of a pure substance are the same. Water for example freezes and melts at 0ºC.

Requires a significant decrease in temperature (or loss of thermal energy) and occurs at a specific temperature which is unique for each pure substance.

Evaporation

When a liquid changes into a gas. Evaporation occurs only at the surface of liquids where high energy particles can escape from the liquid’s surface at low temperatures, below the b.p. of the liquid.

The larger the surface area and the warmer the liquid/surface, the more quickly a liquid can evaporate.

No heat is required and evaporation occurs over a range of temperatures.

Condensation

When a gas changes into a liquid, usually on cooling. When a gas is cooled its particles lose energy and when they bump into each other, they lack energy to bounce away again, instead grouping together to form a liquid.

No energy is required for condensation to occur and it takes place over a range of temperatures.

Sublimation

When a solid changes directly into a gas.

This happens to only a few solids such as iodine or solid carbon dioxide.

The reverse reaction also happens and is also called sublimation (sometimes called deposition or desublimation).

Sublimation occurs at a specific temperature which is unique for a pure substance.

2.4 Predict the physical state of a substance under specified conditions, given suitable data

○ at temperatures below the melting point, the substance will be solid

○ at temperatures above the melting point but below the boiling point, the substance will be liquid

○ at temperatures above the boiling point, the substance will be a gas

● if you are given the melting point and boiling point of a substance: The physical state of a substance under certain conditions can be predicted from a given set of data.