Chemistery

Put a thermometer in a pan of melting ice and watch it. You're pouring heat in, and the reading refuses to move off 0 °C until the last ice cube is gone. Where is all that energy going? The short answer: a phase change is a physical change in which a substance moves between solid, liquid and gas — melting, freezing, boiling, condensing, subliming or depositing. During a phase change the temperature stays constant, because the energy goes into breaking the attractions between particles rather than speeding them up. The six phase changes There are three states, so there are six one-way trips between them: Change From → To Everyday example Melting (fusion) Solid → Liquid Ice turning to water Freezing (solidification) Liquid → Solid Water turning to ice Vaporisation (boiling/evaporation) Liquid → Gas Water becoming steam Condensation Gas → Liquid Mist forming on a cold window Sublimation Solid → Gas Dry ice fogging without melting Deposition ...

Every solution question starts with the same small decision, and it trips up more students than the calculations that follow: which one is the solute and which is the solvent? Get it backwards and your concentration answer is upside down. The short answer: the solute is the substance that gets dissolved ; the solvent is the substance that does the dissolving . Together they make a solution , and the solvent is normally whichever one is present in the greater amount. Quick comparison at a glance Feature Solute Solvent Role Gets dissolved Does the dissolving Amount present Usually the smaller amount Usually the larger amount State after mixing Takes on the solvent's state Keeps its own state Common state Often solid, but can be any Usually liquid Everyday example Salt, sugar, CO₂ Water, ethanol, acetone In salt water Salt (NaCl) Water Changes when mixed? Broken up into particles/ions Stays as it is What a solute is A solute is wha...

Salt vanishes into water in seconds. Oil sits on top and sulks no matter how hard you stir. Sugar dissolves faster in hot tea than iced tea. All three are the same question wearing different clothes: what makes something dissolve? The short answer: solubility is the maximum amount of a substance that will dissolve in a given amount of solvent at a particular temperature. Whether something dissolves comes down to one rule — "like dissolves like" — because polar solvents pull apart polar and ionic solutes, and nonpolar solvents dissolve nonpolar solutes. What solubility actually measures Solubility is a number, not a yes/no. It's usually quoted as grams of solute per 100 g of water at a stated temperature : Table salt, NaCl: about 36 g per 100 g of water at 25 °C Sugar (sucrose): about 200 g per 100 g of water at 20 °C Chalk, CaCO₃: about 0.0013 g per 100 g of water at 25 °C Notice that chalk isn't strictly insoluble — it's just so poorly soluble that w...

Air and water both look like one clear, uniform thing. But one of them you can separate by chilling it, and the other needs electricity to pull apart. That difference — mixture or compound — decides almost everything about how a substance behaves. The short answer: a compound is two or more elements chemically bonded in a fixed ratio, forming a new substance with new properties. A mixture is two or more substances simply physically mixed in any ratio, with each keeping its own properties and no bonds between them. Quick comparison at a glance Feature Mixture Compound What holds it together Nothing — just physical mixing Chemical bonds Ratio of components Any ratio you like Fixed and definite Properties Components keep their own Completely new properties How to separate Physical methods (filtering, distilling, magnets) Chemical methods (electrolysis, reactions) Energy change on forming Little or none Usually significant (heat given out or taken in...

Ice, water and steam are all H₂O. Same molecule, same formula, wildly different behaviour — one you can stand on, one you can pour, one that fills the room. Nothing about the molecule changed. What changed is how the molecules are arranged . The short answer: the states of matter are the physical forms a substance can take — solid, liquid and gas are the three you meet first, with plasma as the fourth. They differ only in how tightly the particles are packed and how freely they move, not in what the particles are. What a "state" actually describes Every state question comes down to a tug-of-war between two things: Attractive forces pulling particles together (the intermolecular forces between molecules, or the bonds holding a giant structure). Kinetic energy — the movement energy of the particles, which rises with temperature and pushes them apart. Heat something up and you give the particles more kinetic energy. When that energy wins, the state changes. Cool it...

Two concentration units, one letter apart, both pronounced almost identically. The difference comes down to a single word in each definition — solution versus solvent — and that one word changes when you'd use each. The short answer: molarity (M) is moles of solute per litre of solution . Molality (m) is moles of solute per kilogram of solvent . Molarity measures the final mixture by volume; molality measures only the solvent, by mass. Quick comparison at a glance Feature Molarity (M) Molality (m) Definition mol solute ÷ L of solution mol solute ÷ kg of solvent Units mol/L mol/kg Denominator measures The whole mixture Only the solvent Measured by Volume Mass Changes with temperature? Yes — liquids expand No — mass is fixed Best used for Titrations, everyday lab work Boiling point and freezing point problems How you prepare it Dissolve, then top up to the mark Weigh solute and solvent separately What is molarity? Molarity is the concentration unit you'll use...