Chemistery

Burn a piece of paper and you cannot get the paper back. Heat blue copper(II) sulfate crystals until they turn white, add water, and the blue returns. Same subject, two completely different kinds of arrow. The short answer: an irreversible reaction goes essentially to completion in one direction and is written with a single arrow (→), while a reversible reaction proceeds in both directions at once, is written with a double half-arrow (⇌), and settles at an equilibrium containing both reactants and products. Quick comparison at a glance Feature Irreversible Reversible Arrow used → ⇌ Direction One way only, in practice Both ways simultaneously End state Reactants (or one of them) fully used up A mixture of reactants and products Reaches equilibrium? No Yes, in a closed system Can products re-form reactants? Not to any measurable extent Yes, continuously Typical examples Combustion, most precipitation, strong acid + strong base Haber process, hydrated salts, weak acid dissocia...

Every particle in a beaker of solution collides with its neighbours trillions of times a second. If every one of those collisions caused a reaction, everything would react instantly and chemistry would be over. It doesn't, and collision theory explains why. The short answer: collision theory says that for particles to react they must collide , and that a collision only works if it has (1) at least the activation energy and (2) the correct orientation . Collisions meeting both conditions are called successful or effective collisions, and they are a small minority. The two conditions Condition 1 — enough energy. Reactions have to break bonds before they can make new ones, and breaking bonds costs energy. The minimum a colliding pair must bring is the activation energy, Eₐ . Below that, the particles simply bounce apart unchanged, however many times they meet. Condition 2 — correct orientation. Molecules aren't featureless spheres. The reactive part has to be pointing the...

If a catalyst speeds a reaction up, an inhibitor must be its mirror image and slow it down, right? Half right — and the half that's wrong is exactly where exam marks get lost. The short answer: a catalyst speeds a reaction up by offering an alternative route with a lower activation energy, and is regenerated unchanged at the end. An inhibitor slows a reaction down — usually by blocking or removing something the reaction depends on — and is very often used up in the process. Quick comparison at a glance Feature Catalyst Inhibitor Effect on rate Increases it Decreases it How it works Provides a lower-activation-energy pathway Blocks a site, removes a reactive intermediate, or poisons a catalyst Consumed overall? No — always regenerated Depends on the type; many are used up Amount needed Tiny, often catalytic traces Usually far more than a catalyst Effect on equilibrium position None None (it changes only how fast equilibrium is reached, if at all) Effect on activation ene...

Rust takes years. A firework takes milliseconds. Both are chemical reactions, and the only difference your exam actually asks about is how fast . That question has a name. The short answer: the reaction rate is how quickly reactants are used up or products are formed, measured as a change in concentration per unit time — usually in mol dm⁻³ s⁻¹ . A fast reaction has a large rate; a slow one has a small rate. What reaction rate actually measures Rate is a speed , and like any speed it's an amount divided by a time: rate = change in concentration ÷ time taken Written with symbols, for a reactant that's being consumed: rate = −Δ[reactant] / Δt and for a product being made: rate = +Δ[product] / Δt The minus sign is bookkeeping, not physics. Reactant concentration falls, so Δ[reactant] is negative; the minus flips it so the rate itself comes out positive. Rates are always quoted as positive numbers. You don't have to use concentration. In the lab you measure whatever...

Ammonia turns red litmus blue, neutralises acids and behaves like a base in every way you can test. It also contains no OH group whatsoever. That awkward fact is the reason chemistry has more than one definition of a base. The short answer: the Arrhenius definition says an acid produces H⁺ ions in water and a base produces OH⁻ ions in water. The Brønsted–Lowry definition is broader: an acid is any proton donor and a base any proton acceptor , which works outside water and explains substances like ammonia that have no hydroxide to give. Quick comparison at a glance Feature Arrhenius Brønsted–Lowry Proposed 1884 1923 Acid is A substance producing H⁺ in water A proton (H⁺) donor Base is A substance producing OH⁻ in water A proton (H⁺) acceptor Requires water? Yes No Covers ammonia as a base? Not under the original definition Yes Covers gas-phase reactions? No Yes Introduces conjugate pairs? No Yes Scope Narrower Broader — includes all Arrhenius acids and bases What the Ar...

You're handed a beaker of acid and told to work out how concentrated it is. You can't weigh it — it's already dissolved. You can't see it. What you can do is find out exactly how much base it takes to cancel it out, and work backwards. That's a titration. The short answer: a titration is a lab technique for finding the unknown concentration of a solution by reacting it with a solution of known concentration, added drop by drop until the reaction is exactly complete. An indicator signals that moment, and the volume used lets you calculate the answer. What a titration actually is The setup is always the same three pieces of glassware: The burette holds the solution you know — the titrant — and lets you add it in measured drops. The conical flask holds the solution you don't know — the analyte — measured out precisely with a pipette. A few drops of indicator go in the flask to signal the finish. You run titrant in slowly, swirling. Near the end you g...