Phenomena
Everyday scientific phenomena explained with living diagrams and concise, carefully checked text. The motion helps show the mechanism; the article explains what the diagram simplifies.
Evaporation
Evaporation is the passage of molecules from the surface of a liquid into the gas phase. Water does not need to boil for this to happen.
Condensation
Condensation is the change from a gas to a liquid. In everyday life, water vapour condensing into tiny droplets is the example we notice most often.
Boiling
Boiling occurs when vapour bubbles can form throughout a liquid and grow instead of collapsing. It is not simply faster evaporation.
Melting
Melting is the transition from solid to liquid. The particles remain the same substance; what changes is the way they are organised and move.
Freezing
Freezing is the transition from liquid to solid. As energy is removed, particles become less mobile and a stable solid structure can form.
Dissolution
When a substance dissolves, its particles disperse among those of the solvent. They have not vanished: they are simply distributed on a scale too small to see directly.
Diffusion
Diffusion is the spontaneous spreading of particles caused by their thermal motion. It tends to reduce concentration differences over time.
Crystallization
Crystallization is the formation of an ordered solid structure from particles that were previously more dispersed, for example in a solution or a melt.
Photosynthesis
Photosynthesis allows plants, algae and some microorganisms to store light energy in chemical form. Carbon dioxide and water provide the raw material for making organic matter, while oxygen is released.
The water cycle
Earth’s water is continually moving between oceans, atmosphere, land, ice, soil and groundwater. The water cycle is this network of transfers and changes of state, not a simple circle followed by every molecule.
Surface tension
Water can behave as if its surface were slightly stretched. The reason is not a real skin, but the way water molecules attract one another.
Capillary action
Water can climb a narrow tube without a pump. Capillary action comes from the competition between attraction to a surface and attraction between water molecules.
Corrosion
Corrosion is a chemical or electrochemical transformation of a material caused by its environment. Rusting iron is the best-known example, but corrosion is much broader than rust.
Acids and bases
Acid–base chemistry is not just about a number on the pH scale. It describes reactions in which protons are transferred and helps explain substances from vinegar to antacids.
Osmosis
Water can cross a selective membrane even when dissolved substances cross it much less easily.
Electrolysis
Electrolysis uses electricity to drive a chemical reaction.
Thermal conduction
Heat can travel through a material without the material itself flowing.
Convection
Convection transfers heat because a liquid or gas moves.
Solubility
Dissolving depends on the substance, the solvent, temperature and sometimes pressure.