Why some reactions happen faster — Chemistry, 7–10 years
Temperature and surface area can change how quickly a chemical reaction happens. This explains why a crushed tablet fizzes faster and why food cooks differently at different temperatures.
The speed of a reaction
Chemical reactions do not all happen at the same speed. Warmth usually makes particles move and meet more often, while smaller pieces give more surface for contact. Both can make a reaction finish sooner.
Why speed matters
People needed to control reactions rather than simply wait for them. A cook wants food to heat quickly but safely, while a medicine maker needs a reaction to happen at a reliable speed. Comparing speeds helps us choose conditions that work.
A fizzy tablet
Put one tablet in 200 millilitres of cold water and time it: it takes 90 seconds. Crush a second tablet into powder and repeat. The powder may finish in 45 seconds because much more of it touches the water, so the reaction has more chances to happen at once.
Fast is not always more
A common mistake is to think that a faster reaction makes more product. Speed tells us how quickly change happens, not how much material there will be at the end. A crushed tablet can finish sooner but still contain exactly the same amount of medicine.
In cooking and storage
A higher oven temperature can make some cooking reactions happen faster, but food can burn if it is too high. Refrigerators slow many chemical changes, which helps food keep its taste and texture for longer. This is why temperature is part of a recipe and a storage label.
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