Changes of State

You're already familiar with the three states of matter - solid, liquid, and gas - but what's brilliant is how substances can transform between these states without changing their chemical identity. When ice melts into water or water boils into steam, you're still dealing with the same H₂O molecules, just arranged differently.

The six main changes of state each have specific names: melting (solid to liquid), freezing (liquid to solid), evaporation (liquid to gas), condensation (gas to liquid), sublimation (solid directly to gas), and deposition (gas directly to solid). These transformations happen when you add or remove energy, usually in the form of heat.

Here's the key point that'll save you marks in exams: these are physical changes, not chemical ones. The substance's identity remains exactly the same - only its state changes. This means the conservation of mass applies perfectly - 100g of ice becomes 100g of water, which becomes 100g of steam.

Quick Tip: Think of sublimation happening with dry ice (solid carbon dioxide) - it goes straight from solid to gas without becoming liquid first!