Chemistery

Diamond is not the most stable form of carbon. Graphite is. Every diamond on Earth is slowly, inevitably turning into pencil lead — and will finish somewhere around the heat death of the universe. That gap between should and does is the whole of this post. The short answer: thermodynamics tells you whether a reaction is energetically favourable and how far it will go; kinetics tells you how fast it gets there. A reaction can be thermodynamically favourable and kinetically impossible at room temperature — which is why diamonds survive. Quick comparison at a glance Feature Thermodynamics Kinetics Question answered Will it happen? How far? How fast will it happen? Key quantities ΔH, ΔS, ΔG, K Rate, activation energy (Eₐ) Depends on Only the start and end states The pathway between them Shown on an energy profile by The difference in height between reactants and products The height of the hump Changed by a catalyst? No Yes Changed by temperature? Yes (ΔG and K both shift) ...

Equilibrium sounds like the reaction has stopped. It hasn't — and that misunderstanding costs more marks in this topic than anything else. The short answer: chemical equilibrium is the state a reversible reaction reaches in a closed system when the forward and reverse reactions are happening at the same rate , so the concentrations of everything stop changing. It is dynamic : both reactions continue indefinitely, they just cancel out. What "dynamic" actually means Picture a sealed flask. At the start there's only reactant, so the forward reaction is fast and the reverse can't happen at all. As product builds up, the forward rate falls (reactant is being used) and the reverse rate rises (there's now product to react back). Sooner or later the two rates meet. From that moment on, product is being made exactly as fast as it's being destroyed, so the amounts stay constant — even though, at the molecular level, nothing has slowed down at all. An analogy...

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...