Chemistery

Manganese dioxide makes hydrogen peroxide fizz into water and oxygen. So does a drop of blood. One is a gritty black powder, the other contains one of the fastest protein machines known — and both are doing the same catalytic job. So is an enzyme just a catalyst with a biology degree, or something more? The short answer: every enzyme is a catalyst, but not every catalyst is an enzyme. A catalyst is anything that speeds up a reaction without being consumed; an enzyme is a biological catalyst — a protein (occasionally RNA) made by a living cell, far bigger, far more specific, and far fussier about temperature and pH than the metals and powders of the chemistry lab. Quick comparison at a glance Feature Enzyme Inorganic (lab) catalyst What it is Protein (rarely RNA) made by cells Usually a metal or simple compound: Fe, Pt, Ni, MnO₂, V₂O₅ Size Enormous — thousands to millions of daltons Tiny — atoms or small formula units Specificity Usually one substrate or reac...

Right now, without you asking it to, your body is running thousands of different chemical reactions — digesting breakfast, copying DNA, turning glucose into energy. Left alone, most of those reactions would take years. Your cells run them in milliseconds, and the machines that make that possible are enzymes. The short answer: an enzyme is a biological catalyst — a molecule, almost always a protein , that speeds up a specific chemical reaction in a living thing by lowering its activation energy, without being used up itself. One enzyme molecule can be reused thousands of times per second. What an enzyme actually is An enzyme is a large molecule — usually a globular protein , a chain of amino acids folded into a precise three-dimensional blob. Somewhere on that blob is a small pocket called the active site , shaped to fit one particular molecule (the substrate ). The substrate binds, the reaction happens, the products leave, and the enzyme is ready to go again: enzyme + substrate ...

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...

Paper doesn't burst into flame just sitting on your desk, even though burning it releases energy. Petrol won't ignite until a spark arrives. Why do reactions that give off energy still need a push to get going? The answer is activation energy — the hidden hurdle in front of every reaction. The short answer: activation energy (Eₐ) is the minimum amount of energy that reacting particles need in order to start a reaction — the energy required to break the initial bonds so new ones can form. It's an energy "hill" the reactants must climb before they can roll down to become products, which is why even energy-releasing reactions need a little energy to begin. Why reactions need a push For particles to react, they have to collide — and not just any collision works. They must hit each other hard enough (with enough energy) and in the right orientation. That minimum energy needed to start rearranging bonds is the activation energy . Picture pushing a boulder over a...

Some reactions that should happen barely crawl along — until you add a pinch of the right substance and they suddenly race. That substance isn't a reactant and it isn't used up. It's a catalyst, and it's one of the most useful tricks in all of chemistry (and biology). The short answer: a catalyst is a substance that speeds up a chemical reaction by providing an easier pathway with a lower activation energy , without being permanently used up itself. Because it's regenerated at the end, a tiny amount of catalyst can help enormous amounts of reactant react, over and over. What a catalyst actually does Every reaction has an energy "hill" the reactants must climb before they can turn into products — the activation energy . A catalyst doesn't push the reactants harder; it offers a lower hill by giving the reaction an alternative route. More reactant particles have enough energy to get over a smaller hill, so the reaction goes faster. An analogy: ima...