Applications & Explore Online രാസപ്രവർത്തനവേഗം

Controlling the rate of a reaction is everyday work. We slow reactions down when we keep fish in ice, salt mangoes for pickle or paint an iron gate before the monsoon. We speed them up when we split firewood, leave the dosa batter out overnight, chew our rice well, or let a catalyst make ammonia for fertilisers. Every section below has a small animation, the factor at work, and a sample exam question. The page ends with a hub of links to explore online.

1. Fish in ice, salted fish and mango pickle: slowing decay

temperature · water · air Fish, milk and cooked rice spoil because of chemical reactions: microbes and their enzymes break the food down, and oils react with the oxygen of the air and go rancid. Food preservation പ്രിസർവേറ്റീവുകൾ means slowing these reactions down. Fish sellers pack fish in ice and we keep food in the refrigerator: at a low temperature the particles have less kinetic energy, fewer reach the threshold energy, and decay is slow. Salting fish, making mango pickle with salt and vinegar, drying in the sun and storing in sugar syrup take away the water microbes need. Vacuum packing keeps oxygen away. Permitted preservatives are chemicals that slow spoiling.

2. Dosa batter and curd: warm days ferment faster

temperature Grind rice and urad dal at night and by morning the batter has risen and smells sour. This fermentation is a chemical change done by the enzymes എൻസൈമുകൾ of yeast and bacteria; the bubbles are carbon dioxide. In the summer the batter rises in a few hours; on a cold rainy night it takes much longer; in the fridge it hardly changes. Curd sets the same way: warm milk with a spoon of curd sets by morning, and we put the curd in the fridge to slow further souring. go further Too much heat (above about 45 °C) kills the microbes, so the batter is kept warm, never hot.

3. Pressure cooker: hotter water cooks faster go further

temperature Cooking rice, dal or meat is a set of chemical changes in starch and proteins. In an open pot the water cannot get hotter than its boiling point, 100 °C. In a pressure cooker the steam is trapped, the pressure rises, and the water boils at about 120 °C. At the higher temperature the cooking reactions are much faster, so dal that takes about an hour in an open pot is ready in a few whistles. At hill stations like Munnar water boils a little below 100 °C, so cooking in an open pot is slower there.

4. Split firewood and kindling

surface area A thick log is hard to light and burns slowly; the same wood split into small pieces catches fire easily and burns fast; thin dry twigs and coconut husk (kindling) flare up at once. Burning is a reaction between wood and the oxygen of the air, and it can happen only at the surface of the wood. Splitting the wood increases the surface area പ്രതലപരപ്പളവ്, so more oxygen particles collide with the wood every second. Fanning the fire or blowing through a pipe adds more oxygen (concentration).

5. Vishu and Onam fireworks: magnesium powder

surface area A magnesium ribbon burns steadily with a dazzling white flame. In fireworks, magnesium (and aluminium) are used as a fine powder: its huge surface area lets the metal react with oxygen almost at once, giving a brilliant flash. The same idea explains why fine coal dust in mines and flour dust in mills can explode go further.

6. Car air bags: a decomposition in 0.03 s

a very fast reaction In a crash, a sensor sends an electric spark into a small charge of sodium azide. It decomposes at once: 2NaN₃ → 2Na + 3N₂↑. The nitrogen gas fills the nylon bag in about 0.03 s, faster than a blink, so the bag is ready before the person is thrown forward. This is a decomposition reaction വിഘടന രാസപ്രവർത്തനം, and here the high rate is exactly what saves lives. go further Other chemicals in the unit make the reactive sodium harmless.

7. Catalytic converters in vehicles go further

catalyst Car and bike exhaust contains poisonous carbon monoxide (CO), nitrogen oxides (NO) and unburnt fuel. In the exhaust pipe of modern vehicles sits a catalytic converter: a honeycomb coated with tiny amounts of the metals platinum, palladium and rhodium. On their huge surface the harmful gases are changed quickly into carbon dioxide, nitrogen and water. The metals are catalysts ഉൽപ്രേരകം: they are not used up, so one converter works for years. The honeycomb shape gives a large surface area too.

8. Chew your rice: amylase in saliva

enzyme (catalyst) · surface area Keep a mouthful of rice in your mouth and chew it for a minute: it starts to taste sweet. Saliva contains the enzyme amylase, a biological catalyst that speeds up the breakdown of starch into the sugar maltose. Chewing well breaks the food into small bits (more surface area for the enzyme), and our body temperature, about 37 °C, suits the enzyme. Without enzymes, digestion would take far too long for life. Enzymes in nature even power the hot spray of the bombardier beetle, which decomposes hydrogen peroxide very fast (textbook box).

9. Ammonia for fertilisers: the Haber process

catalyst · temperature · pressure Ammonia is made from nitrogen (from the air) and hydrogen by the Haber process ഹേബർ പ്രക്രിയ: N₂(g) + 3H₂(g) ⇌ 2NH₃(g). At room temperature the reaction is far too slow to be useful. Industry uses iron (Fe) as the catalyst, a pressure of about 200 atm and a temperature of about 700 K. The sign ⇌ means the reaction is reversible ഉഭയദിശാ പ്രവർത്തനങ്ങൾ, so the unreacted gases are sent round again. Ammonia is turned into fertilisers such as ammonium sulphate and urea; in Kerala, fertiliser factories such as FACT at Udyogamandal make ammonia-based fertilisers. In the contact process സമ്പർക്ക പ്രക്രിയ for sulphuric acid, 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) is speeded up by vanadium pentoxide (V₂O₅) at about 2 atm and 720 K.

10. Welding railway lines with thermite

a very fast displacement Long welded rails make the train ride smooth. To join two rails, workers place a mould around the gap and set off a thermite തെർമൈറ്റ് mixture of aluminium powder and iron oxide in a crucible above it: Fe₂O₃ + 2Al → 2Fe + Al₂O₃. Aluminium displaces iron from its oxide (a displacement reaction ആദേശ രാസപ്രവർത്തനം). Once started, the reaction is so fast and gives out so much heat that the iron formed is molten; it runs down into the gap and welds the rails together. The fine powders help it go fast.

11. Rust prevention: slowing down a slow reaction

contact · moisture Rusting തുരുമ്പിക്കൽ of iron is slow, but over months it eats gates, bicycles and tin roofs. It needs both oxygen and water to reach the iron surface, so it is fastest in our humid monsoon, and near the sea, where salt speeds it up further. We slow it by stopping those collisions: painting gates and grills, oiling or greasing chains and tools, galvanising (a zinc coat, as on GI sheets), and keeping tools dry.

🌐 Explore online – resources hub

Everything in this guide works offline. The links below are extras: a simulation and articles from trusted sources, grouped by topic. They need internet and open in a new tab, so you will not lose your place here. Ask a parent or teacher before you go online.

Types of chemical reactions

Rate of reaction

Collision theory and threshold energy

Catalysts and enzymes

More to explore