Summary & Quick Quiz രാസഗതികം
The whole chapter on one page: chemical kinetics in five pictures, the key boxes of the textbook, every rule you need – the signs of a chemical change, the four types of reactions, collision theory and threshold energy, the five factors that change the rate, catalysts and enzymes – a reaction-type checker, the mistakes to avoid, flashcards, a scored quiz and your study checklist.
1. The chapter in five pictures
2. The key boxes of the textbook
Two or more simple substances (elements or compounds) combine to form a new compound: N2 + 3H2 → 2NH3. – page 4
A compound breaks down to form two or more substances: CaCO3 → CaO + CO2. – page 4
Two compounds react by exchanging ions to form two new compounds: NaCl + AgNO3 → AgCl↓ + NaNO3. – page 5
One element in a compound is replaced by another element: Zn + 2HCl → ZnCl2 + H2↑. – page 5
Substances that increase the rate of a reaction without themselves undergoing a permanent chemical change are catalysts: MnO2 in 2H2O2 → 2H2O + O2. – page 8
In a crash, sodium azide decomposes in about 0.03 s: 2NaN3 → 2Na + 3N2↑ – the nitrogen fills the bag. – page 4
Those giving a precipitate, those giving a gas, and those giving a compound that does not split into ions, such as water in neutralisation. – page 5
Fe2O3 + 2Al → 2Fe + Al2O3 – so much heat that the iron formed is molten; used to weld rails. – page 5
Reactions happen when reactant particles collide; only collisions with enough energy give products – effective collisions. – page 6
White phosphorus catches fire in air at room temperature; red phosphorus does not – the nature of the reactant decides the rate. – page 7
Solid ZnSO4 and Ba(NO3)2 do not react; their solutions give white BaSO4 at once. Petrol vapour explodes. – page 7
Batter ferments faster in warm weather than in the fridge; light sticks glow brighter when warm. – page 8
Enzymes are biological catalysts: amylase in saliva changes starch into maltose. – page 8
A sugar cube burns only with a little ash on it (metal compounds in ash act as a catalyst). The bombardier beetle sprays a hot liquid made by enzyme-catalysed decomposition of hydrogen peroxide. – page 8
3. Facts & rules
📐 Facts & rules card
factor → more collisions, or more particles with ≥ threshold energy → more effective collisions → faster
catalyst → faster, and left unchanged at the end
Physical and chemical changes ഭൗതികമാറ്റം · രാസമാറ്റം
In a chemical change new substances form, usually with an energy change. Signs: colour change (നിറവ്യത്യാസം) – sugar turns black on heating; a gas (വാതകം) – Na2CO3 + HCl fizzes; a precipitate (അവക്ഷിപ്തം) – lead acetate + KI gives yellow lead iodide (teacher demonstration only – lead compounds are poisonous); a smell (ഗന്ധം) – iron sulphide + HCl gives rotten-egg H2S (teacher only, in a fume cupboard – H2S is poisonous); heat – quicklime + water (exothermic, താപമോചക പ്രവർത്തനം). Melting, boiling and dissolving are physical changes.
The four types of reactions രാസപ്രവർത്തനം
| Type | Pattern | What happens | Examples |
|---|---|---|---|
| Combination സംയോജന രാസപ്രവർത്തനം | A + B → AB | two or more substances join to give one product | CaO + H2O → Ca(OH)2; N2 + 3H2 → 2NH3; 2SO2 + O2 → 2SO3 |
| Decomposition വിഘടന രാസപ്രവർത്തനം | AB → A + B | one compound breaks into two or more products (by heat: thermal decomposition, താപീയ വിഘടനം) | CaCO3 → CaO + CO2; CuCO3 → CuO + CO2; 2NaN3 → 2Na + 3N2 |
| Double decomposition ദ്വിവിഘടന രാസപ്രവർത്തനം | AB + CD → AD + CB | two compounds exchange ions; a precipitate, a gas or water forms | NaCl + AgNO3 → AgCl↓ + NaNO3; CaCO3 + 2HCl → CaCl2 + H2O + CO2↑; HCl + NaOH → NaCl + H2O |
| Displacement ആദേശ രാസപ്രവർത്തനം | A + BC → AC + B | an element replaces another element in a compound | Zn + 2HCl → ZnCl2 + H2↑; Fe + CuSO4 → FeSO4 + Cu; Fe2O3 + 2Al → 2Fe + Al2O3 |
Quick test: count the reactants and products and look for a free element. One product → combination; one reactant → decomposition; an element on each side → displacement; two compounds → two (or more) compounds → double decomposition.
The checker first counts the atoms (is it balanced?) and then applies the quick test above, exactly as you would in the exam.
Rate of reaction and collision theory രാസപ്രവർത്തനവേഗം · കൊളിഷൻ സിദ്ധാന്തം
Reactions go at very different speeds: an explosion (സ്ഫോടനം) is over in a moment, a dental filling sets in minutes, rusting (തുരുമ്പിക്കൽ) takes days to months, weathering of rocks takes years. We slow down food spoiling with salting, preservatives (പ്രിസർവേറ്റീവുകൾ), refrigeration, drying, vacuum packing and pickling.
The five factors രാസപ്രവർത്തനവേഗം
| Factor | Example from the book | Reason (collision theory) |
|---|---|---|
| 1. Nature of reactants അഭികാരകങ്ങളുടെ സ്വഭാവം | dilute HCl: Mg fast, Zn slow, Cu no reaction; Na reacts violently with water, Mg very slowly; white P catches fire in air, red P does not | some substances give or take electrons, or break their bonds, much more easily |
| 2. Concentration ഗാഢത | Mg ribbon fizzes faster in concentrated HCl than in dilute (ഗാഢ · നേർപ്പിച്ച); steel wool burns with sparks in pure oxygen | more particles per unit volume (യൂണിറ്റ് വ്യാപ്തം) → more collisions → more effective collisions |
| 3. Surface area പ്രതലപരപ്പളവ് | marble powder faster than a lump; eggshell powder; split firewood; magnesium powder in fireworks; solutions react faster than solids (ഭൗതികാവസ്ഥ) | more particles exposed → more collisions at the same time |
| 4. Temperature താപനില | NH4Cl + NaOH: ammonia smell stronger on warming; thiosulphate + HCl turns cloudy sooner when warm; batter ferments faster in warm weather | more kinetic energy → more particles reach the threshold energy → more effective collisions |
| 5. Catalyst ഉൽപ്രേരകം | MnO2 makes H2O2 give oxygen fast (the glowing incense stick bursts into flame); MnO2 is filtered off unchanged | it increases the rate and is left unchanged (it provides an easier path – go further) |
Catalysts in industry and in living things ഹേബർ പ്രക്രിയ · സമ്പർക്ക പ്രക്രിയ · എൻസൈമുകൾ
| Process | Equation | Catalyst | Conditions |
|---|---|---|---|
| Haber process (ammonia) | N2(g) + 3H2(g) ⇌ 2NH3(g) | iron (Fe) | 200 atm, 700 K |
| Contact process (sulphuric acid) | 2SO2(g) + O2(g) ⇌ 2SO3(g) | vanadium pentoxide (V2O5) | 2 atm, 720 K |
| Digestion | starch → maltose | amylase (an enzyme) in saliva | body temperature |
⇌ marks a reversible reaction (ഉഭയദിശാ പ്രവർത്തനങ്ങൾ): the products also change back into the reactants at the same time. Enzymes (എൻസൈമുകൾ) are biological catalysts.
- Calling dissolving sugar or boiling water a chemical change. No new substance forms – these are physical changes.
- Mixing up decomposition and double decomposition. Decomposition has one reactant; in double decomposition two compounds exchange ions.
- Calling Zn + 2HCl → ZnCl2 + H2 a combination reaction. Zinc replaces hydrogen – it is displacement.
- Thinking a catalyst is used up or changes the products. It is recovered unchanged; it only changes the rate.
- Saying every collision gives products. Only effective collisions, with at least the threshold energy, do.
- Thinking a big lump reacts faster because there is “more” of it. The powder reacts faster – it has more surface area.
- Confusing the amount of product with the rate. More reactant gives more product; a faster rate gives it sooner.
- Saying a higher temperature lowers the threshold energy. It gives more particles enough energy; a catalyst is what provides an easier path.
4. Flashcards
Click a card to flip it.
5. Scored quiz
Answer all sixteen, then press Check my answers. Each wrong answer shows the page to revise. For number answers type only the number.
6. Your study checklist
Ticks come from “Mark this page as completed” at the bottom of each page.
Next: the model test paper ▶ – attempt it on paper with a timer first, then check with the solved paper.