sci_chem
Catalysts
Chapter summary, hard words and model exam answers for ICSE Class 10 Hindi.
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Chemistry · CBSE 10 · ICSE 10 · GCSE (AQA, Edexcel, OCR)
Summary
It lowers the activation energy, so more colliding particles have enough energy to react. The reaction goes faster, but the products and the overall energy change (ΔH) are exactly the same.
A homogeneous catalyst mixes in (e.g. acid in solution). A heterogeneous catalyst is usually a solid, so reactants must stick to (adsorb on) its surface - a big surface area helps.
They work in mild conditions (around 37 °C, near-neutral pH). Too much heat or extreme pH denatures them: the active site changes shape and stops working.
Iron in the Haber process and vanadium(V) oxide in the Contact process are examples. Impurities like sulfur can poison a catalyst by blocking its active sites, so feedstock is purified first.
Hard words & meanings
| catalyst | a substance that speeds up a reaction by lowering activation energy, without being consumed |
| activation energy | the minimum energy colliding particles need to react |
| homogeneous catalyst | a catalyst in the same phase as the reactants |
| heterogeneous catalyst | a catalyst in a different phase, usually a solid, working at its surface |
| adsorption | the sticking of reactant molecules onto a catalyst's surface |
| enzyme | a biological catalyst made of protein |
| active site | the shaped region of an enzyme where the substrate binds |
| catalyst poisoning | loss of activity when impurities block the active sites |
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