Difference between Solid, Liquid and Gas

Solid, liquid and gas are the three fundamental states of matter. The existence of the three states of matter is due to equilibrium achieved by thermal energy and intermolecular forces prevailing in solids, liquid and gaseous phases.

Solid: A substance is said to be in a solid form when disruptive thermal energy is predominated by high intermolecular energy.

Liquid: It is an intermediate phase existing between solid and gaseous phases.

Gas: It is the intermediate phase that exists between the liquid and plasma state of matter.

• The following are the basis on which we distinguish solid, liquid and gas.

Based on Arrangement or Positioning of Molecules

• In the solid phase, atoms or molecules are bound tightly with each other, leaving negligible intermolecular spaces. The molecules could be arranged in a regular or irregular fashion as in crystalline solid and amorphous solid respectively.
• In the liquid phase, molecules are arranged in a random fashion and firmly bounded.
• The gaseous phase has the maximum degree of freedom for molecules. They are widely separated from each other.

Based on Strength of Intermolecular forces

Intermolecular forces refer to the forces of attraction and repulsion that are present in between different molecules interacting with each other. Variation in these forces is observed in different states of matter.

• Solids: High strength of intermolecular forces. It means less distance or gap between each molecule hence resulting in a close-packed/ compact arrangement of solid substances
• Liquids: In contrast to solids, liquids have comparatively less strength of intermolecular forces. The particles are held in the aggregation but not in a fixed position as seen in solids
• Gas: They have weak intermolecular forces between them hence exhibiting random particle motion

Based on Thermal Energy of Molecule

Movement of atoms and molecules causes the generation of thermal energy. The motion of molecules caused by the possession of thermal energy is called thermal motion.

The notable point is thermal energy and intermolecular forces act antagonistically to each other. Simply, the intermolecular forces tend to bring molecules in vicinity whereas thermal energy tends to keep them apart.

• The order of predominance of thermal energy is gas followed by liquid and solid phase

Based on Physical and Mechanical Properties

The mechanical characteristics of substances refer to properties such as their ability to withstand deforming forces.

• In the case of solids, they exhibit good elasticity, have great tensile power, ductility and high compressive strength. Solids show plasticity i.e. can undergo permanent deformation on the application of excessive stress
• The mechanical properties of liquids are in the context of their volume, pressure, fluidity/flow. Liquids have minimal compressibility. Liquids exert pressure on the walls of the vessels they are kept in owing to random particle motion. Liquids show an additional property of buoyancy. In reference to flow, the term viscosity comes into play. The viscosity of any liquid is its ability to resist flow
• Gaseous substances have physical properties namely volume, pressure and temperature

• Volume: Solid, liquid and gas have a definite, somewhat definite and indefinite measure of volume respectively because of different intermolecular forces and molecular arrangement
• Compressibility: Solids being compact, are less likely to compress on pressure. Liquids can be compressed to some extent but in conditions of high pressure or elevated temperature
• Fluidity: solids do not exhibit flow. Because of their compact arrangement and geometry. Liquids are known to ‘flow easily’. Their molecular arrangement allows the liquid to flow. Gases also exhibit flow property owing to the molecules that have high kinetic energy

Based on Density of the Matter

• Solid substances usually possess more density owing to their close-packed structure and definite measure of volume
• Liquid substance is less done in contrast to solids
• Gaseous molecules are less dense or lighter in weight because the number of molecules per unit area is quite low because of the random and large distance between the molecule

The descending order of density possessed by the molecules is solid, followed by liquid and then gaseous matter.

Based on Expansion on Application of Heat

• Gaseous molecules show the maximum degree of expansion when subjected to conditions of heat
• Liquid molecules show expansion to a considerable extent when subjected to heat
• Usually, the molecules of a solid substance don’t expand on heat application

Hence, the order of expansion on heat application is higher in the gaseous phase, followed by liquid and then solid state.

Phase Transitions

The states of matter undergo transition among themselves by the following process:

• Melting: transition from solid to liquid state
• Sublimation: transition from solid to gaseous state
• Freezing: transition from the liquid state to a solid-state
• Condensation: transition from gas to liquid phase
• Vaporisation: transition from the liquid phase to gas phase

These are called phase transitions.

Conclusion

The three fundamental forms in which matter exists in the surrounding area are solid-state, liquid and gaseous state.

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