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States of matter for Edexcel GCSE Chemistry

States of matter

This page covers the following topics:

1. Solids
2. Liquids
3. Gases
4. State symbols
5. Changes of state

Solids are formed when a substance is cooled to below its melting point. Particles in a solid don't have enough energy to break away from a lattice; thus, they can be modelled as tightly packed spheres. Due to little empty space within the lattice, many solids cannot be compressed. Although in most cases the structure within a solid does not change, depending on the temperature, solid particles can still slightly vibrate.

Solids

Liquids are formed when a substance is held above its melting point but below its boiling point. Particles in a liquid have enough energy to partially break their intermolecular forces or bonds, giving them more flexibility to move around in a liquid that results in a higher fluidity. Due to little empty space within liquids, many of them cannot be compressed.

Liquids

Gases are formed when a substance is warmed to above its boiling point. Particles in gases have high enough energy to break their intermolecular forces or bonds, giving them the freedom to move around in space. Due to plenty of empty space within gases, they can be compressed and have low density.

Gases

When writing chemical equations, state symbols are used to indicate which physical state each compound is in. They are written in brackets in subscript after a formula by using (s) for solid, (l) for liquid, (g) for gas and (aq) for aqueous, that is, dissolved in a solution. For example, C(s) + Oโ‚‚(g) โ†’ COโ‚‚(g). Some examples of how these symbols can be used are provided below.

โ‹… compounds dissolved in a solution โ†’ (aq)
โ‹… water in a neutralisation reaction โ†’ (l)
โ‹… insoluble precipitate โ†’ (s)
โ‹… gas insoluble in a solution โ†’ (g)
โ‹… most metals at room temperature โ†’ (s)
โ‹… most pure salts at room temperature โ†’ (s)

State symbols

Substances can change their physical state via a range of physical processes. When a material goes from solid to liquid, its particles start vibrating faster until they have enough energy to escape a lattice and start moving freely around other particles forming an irregular structure. When a substance goes from liquid to gas, its particles get high enough energy to break their intermolecular forces or bonds, giving them the freedom to move around in space. Similar vice versa changes happen backwards with particles starting to form bonds and forces when a material is condensing and particles forming a lattice with stronger interactions or bonds when freezing.

Changes of state

1

Why do liquids have move fluidity than a solid?

Particles in a liquid have enough energy to partially break their intermolecular forces or bonds, giving them more flexibility to move around in a liquid that results in a higher fluidity.

enough energy to break forces or bonds โ†’ higher flexibility & fluidity

Why do liquids have move fluidity than a solid?

2

Describe the motion of particles in a solid.

Particles in a solid don't have enough energy to break away from a lattice; thus, they can be modelled as tightly packed spheres. Although in most cases the structure within a solid does not change, depending on the temperature, solid particles can still slightly vibrate.

Particles in a solid vibrate within a lattice.

Describe the motion of particles in a solid.

3

Include the state symbols to the following equation:

CHโ‚„ + 2Oโ‚‚ โ†’ COโ‚‚ + 2Hโ‚‚O.

All of the reactants and products participating in this reaction are gases, including water that becomes gas due to the reaction being exothermic. However, a liquid state may be assigned to water while, for example, considering enthalpy.

CHโ‚„(g) + 2Oโ‚‚(g) โ†’ COโ‚‚(g) + 2Hโ‚‚O(g)

Include the state symbols to the following equation: 

CHโ‚„ + 2Oโ‚‚ โ†’ COโ‚‚ + 2Hโ‚‚O.

4

Draw a sketch of molten sulphur, showing how its atoms are arranged.

image

Draw a sketch of molten sulphur, showing how its atoms are arranged.

5

After a shower, the steam produced transforms into water when in contact with a cold surface. What physical process is described in the previous sentence?

Condensation is a process during which a material is converted from a gas to a liquid state.

condensation

After a shower, the steam produced transforms into water when in contact with a cold surface. What physical process is described in the previous sentence?

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