Using rate of reaction in daily life
Once we understand what changes the rate of reaction, we can control reactions to make life easier, safer and cheaper. Many everyday actions are really about speeding a useful reaction up or slowing an unwanted one down.
Slowing reactions down
- Refrigeration — keeping food cold lowers the temperature, so the reactions of bacteria that spoil food happen very slowly. Freezing is even more effective.
- Storing reactive chemicals cool and in low concentration reduces the chance of unwanted fast reactions.
- Adding preservatives or salt to food, as in salted fish, slows the reactions caused by spoilage microbes so the food keeps longer.
Speeding reactions up
- Pressure cooker — cooking under pressure raises the boiling temperature above 100°C, so food such as beef rendang cooks faster.
- Powdered ingredients — powdered sugar or fine flour dissolves and reacts faster than large lumps because of the larger surface area.
- Catalysts in industry — an iron catalyst speeds up the Haber process (making ammonia), while vanadium(V) oxide is used in the Contact process (making sulphuric acid). A catalytic converter in a car uses platinum to speed up the change of harmful gases into safer ones.
- Enzymes, which are natural catalysts, are added to washing powders so that stains break down faster even in warm water.
Example
Charcoal for a barbecue is broken into small pieces rather than left as one large block, so the larger surface area lets it catch fire and burn faster.
Key idea
Lower temperature and lower concentration slow reactions (good for storage); higher temperature, larger surface area and catalysts speed reactions up (good for cooking and industry).
Remember
Very fine powders, such as flour dust in a mill, can react with air so fast that they cause a dangerous dust explosion.