STATES OF MATTER - properties of gases and liquids (fluids) and solids

1. Introduction to the three states of matter

GCSE (~US grades 8-10) level multiple choice QUIZ on the states of matter: gases, liquids & solids

Part 1 Introduction to the three states of matter

You should know that the three states of matter are solid, liquid and gas. Melting and freezing take place at the melting point, boiling and condensing take place at the boiling point. The three states of matter can be represented by a simple model in which the particles are represented by small solid spheres. Particle theory can help to explain melting, boiling, freezing and condensing.

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 and the nature of the particles involved depends on the type of bonding and the structure of the substance. The stronger the forces between the particles the higher the melting point and boiling point of the substance.

See Part 14. Comparison of latent heat changes in physical changes of state for different types of structure and for more details see  structure and bonding notes.

The strength of the forces between particles depends on the material (structure and type of bonding), the temperature (affects the energy of the particles) and pressure (how close the particles are compressed together e.g. in a gas).

The physical state a material adopts depends on its structure, temperature and pressure.

State symbols used in equations: (g) gas      (l) liquid     (aq) aqueous solution     (s) solid

aqueous solution means something dissolved in water,

a good example of how to use the state symbols correctly is calcium carbonate dissolving in hydrochloric acid, which uses all four state symbols:

CaCO₃(s)  +  2HCl(aq)  ====>  CaCl₂(aq)  +  H₂O(l)  +  CO₂(g)

Most diagrams of particles are often 2D representations of their structure and state

EXAMPLES OF THE THREE PHYSICAL STATES OF MATTER

GASES

e.g. the air mixture around us (including the oxygen needed for combustion) and the high pressure steam in the boiler and cylinders of the steam locomotive.

All of the gases in air are 'invisible', being colourless and transparent.

Note that the 'steam' you see outside of a kettle or steam locomotive is actually fine liquid droplets of condensed water, formed from the expelled steam gas condensing when it meets the cold air – the 'state change' of gas to liquid (same effect in mist and fog formation).

LIQUIDS

e.g. water is the most common example, but so are, milk, hot butter, petrol, oil, mercury or alcohol in a thermometer, lots of everyday materials.

All solutions are liquids.

SOLIDS

e.g. stone, all metal objects at room temperature (except mercury), wood, rubber of walking boots, plastic materials i.e. the majority of physical objects around you!

In fact most objects are useless unless they have a solid structure!

In later sections

The basic physical properties of gases, liquids and solids are described in terms of structure, particle movement (kinetic particle theory), effects of temperature and pressure changes, and particle models used to explain these properties and characteristics.

Hopefully, theory and fact will match up to give students a clear understanding of the material world around them in terms of gases, liquids and solids – referred to as the three physical states of matter.

The changes of state known as melting, fusing, boiling, evaporating, condensing, liquefying, freezing, solidifying, crystallising are described and explained with particle model pictures to help understanding.

There is also a mention of miscible and immiscible liquids and explaining the terms volatile and volatility when applied to a liquid.

The details are discussed in the following sections (also listed in the index)

2. Three states of matter - what can we expect from particle models and are there limitations?

3. A kinetic particle model of a gas, properties, pressure and the effect of temperature change

4. What is diffusion? Particle model and examples of demonstrating diffusion in gases

5. Kinetic particle model of a liquid and properties explained, 2nd mention of Brownian motion

6. Particle model of a liquid and diffusion experiments and associated phenomena

7. Particle model of a solid and explaining the properties of solids, links to physics density notes

More on examples of gases, liquids and solids, the three states of matter

• Gases: Oxygen (O₂), Hydrogen (H₂), Carbon dioxide (CO₂), Ammonia (NH₃), Chlorine (Cl₂)
• Liquids: Water (H₂O), Ethanol (C₂H₅OH), Bromine (Br₂), Hydrochloric acid (HCl aq)
• Solids: Sodium chloride (NaCl), Diamond (C), Graphite (C), Sulfur (S₈), Metals (Fe, Cu, Al)
• Note that they do not have to be pure elements or pure compounds e.g. air is a mixture of gases, all solutions are mixtures and all alloys are a mixture of metals and other compounds.
• You need to be able to interpret the particle pictures illustrated above.

Properties (much more detail in parts 2 to 7)

Industrial Manufacture of important gases

• Oxygen: Fractional distillation of liquid air
• Hydrogen: Steam reforming of methane, electrolysis of water
• Carbon dioxide: By-product of fermentation, neutralization reactions
• Ammonia: Haber process → NH₃) (iron catalyst, 450°C, 200 atm)
• Sulfuric acid (liquid): Contact process → SO₂ → SO₃ → H₂SO₄

Examples of Uses of gases

• Oxygen: Medical use, welding, steel manufacture
• Hydrogen: Fuel cells, margarine manufacture (hydrogenation)
• Carbon dioxide: Fire extinguishers, fizzy drinks, refrigeration (dry ice)
• Ammonia: Fertilizers (ammonium nitrate), cleaning products

Exam Tips

• Link particle theory to macroscopic properties (compressibility, diffusion).
• For industrial processes, quote conditions (temperature, pressure, catalyst).

Common Misconceptions

• Thinking solids cannot diffuse → they can, but very slowly (e.g., diffusion of gases through solids).
• Believing liquids are easily compressed → they are not.
• Confusing test for oxygen versus hydrogen (splint test differences).
• Forgetting that ionic solids conduct electricity only when molten or dissolved, not when solid.

Learning objectives for particle pictures and an introduction to the states of matter

Know that matter can exist in a solid, liquid and gaseous state and recognise the state from a given description or picture of a material.

Be able to recognise from particle pictures whether the substance is a solid, liquid or gas and also deduce whether it is a particle picture of a pure element, a pure compound or a mixture of elements or compounds.

All my UK advanced level (~US grades 11-12) pre-university chemistry revision notes

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