Chemistery

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...

Reactions almost never come with perfectly matched ingredients. One runs out, the rest sits there unused — and the one that runs out decides everything about how much product you get. The short answer: the limiting reactant is the reactant that is completely used up first, so it sets the maximum amount of product the reaction can make. Any reactant still left over when the reaction stops is the excess reactant . The sandwich analogy You have 10 slices of bread and 8 slices of cheese , and each sandwich needs 2 bread + 1 cheese . Bread allows 10 ÷ 2 = 5 sandwiches Cheese allows 8 ÷ 1 = 8 sandwiches You can only make 5 . Bread is limiting; 3 slices of cheese are left over — the excess. Notice you had more bread than cheese by count, and bread still ran out first. That's the whole lesson: it isn't about which you have most of, it's about how fast the recipe consumes each one. In chemistry, the "recipe" is the balanced equation's coefficients. How to...

You do the stoichiometry, the equation says you should get 28.0 g, and the balance says 24.5 g. Nothing has gone wrong — that's just chemistry in a real flask. These two yields are how chemists describe that gap. The short answer: theoretical yield is the maximum amount of product a balanced equation predicts if everything reacts perfectly. Percent yield compares what you actually collected to that maximum: percent yield = (actual yield ÷ theoretical yield) × 100% . Quick comparison at a glance Feature Theoretical yield Percent yield What it is The predicted maximum product How efficient the reaction was Where it comes from Calculation from the balanced equation Comparing lab result to prediction Units Grams or moles Percent — no units Needs lab work? No, it's pure calculation Yes, you need the actual yield Based on The limiting reactant Actual ÷ theoretical Typical value A fixed number, e.g. 28.0 g Usually 70–90%; never above 100% There's a third term hiding ...

Stoichiometry sounds like the hardest word in the chapter and turns out to be the most mechanical part of it. It's a recipe calculation: if this much goes in, how much comes out? Once you learn one route through it, every problem uses the same route. The short answer: stoichiometry is using the coefficients of a balanced chemical equation as a mole ratio to work out how much of one substance reacts with, or is produced by, another. The coefficients compare moles , never grams — which is why every problem passes through moles on the way. What the coefficients actually tell you Take the reaction that makes ammonia: N₂ + 3 H₂ → 2 NH₃ Read it as a ratio: 1 mole of N₂ reacts with 3 moles of H₂ to make 2 moles of NH₃. That's the mole ratio, and it comes free with a balanced equation. What it does not say is that 1 gram of N₂ reacts with 3 grams of H₂. Different substances have different molar masses, so grams don't scale that way. Coefficients count particles, not we...