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Investigate chemical reactions that happen over a long period of time.
Have you ever wondered why a shiny new bicycle left out in the rain turns orange and crumbly after a few weeks?
Rust isn't just dirt or orange paint; it is the result of a chemical change. When objects made of iron () are exposed to oxygen () and water (), a reaction occurs. The iron atoms bond with oxygen atoms to create a brand new substance called iron oxide (). This specific type of chemical reaction is called oxidation. Unlike some reactions that happen in a flash, oxidation is usually a slow change that eats away at the metal over days, weeks, or even years. This process of wearing away metal is also known as corrosion.
Quick Check
What are the three essential 'ingredients' needed for rust to form?
Answer
Iron, oxygen, and water.
All chemical reactions involve energy, but they don't all happen at the same speed. Think of a burning match. This is a fast chemical change called combustion. It releases its energy as heat and light in just a few seconds. Rusting is very different. It is a slow chemical change. It still releases energy as it happens, but it happens so slowly that you cannot feel the heat. If we used a formula to look at the 'speed' of these reactions, the rate of a match burning is thousands of times higher than the rate of a nail rusting.
Imagine you find an old iron nail in a garden. 1. The nail was originally shiny silver (). 2. It sat in the damp soil (providing and ). 3. Over months, the surface turned into brittle, orange powder (). This is a classic example of slow oxidation.
Quick Check
How does the energy release of a burning match differ from a rusting iron pipe?
Answer
A match releases energy quickly as heat and light, while rust releases energy so slowly that the temperature change is unnoticeable.
Because rust makes metal weak and crumbly, engineers have to find ways to stop it. The secret to stopping rust is to create a barrier that prevents oxygen and water from touching the iron. Common methods include painting (like on a bridge), oiling (like on a bike chain), or galvanizing, which is coating the iron in a thin layer of a different metal like zinc () that doesn't rust as easily. If the 'ingredients' can't meet, the chemical reaction simply cannot start!
The Golden Gate Bridge is made of steel (which is mostly iron). Because it sits over the salty ocean, it is at constant risk of rusting. 1. Saltwater acts like a 'turbo-charger' for oxidation, making it happen faster. 2. To prevent the bridge from falling apart, teams of painters apply special 'International Orange' paint year-round. 3. This paint acts as a waterproof shield, blocking and from reaching the steel.
Predict which car will rust faster: Scenario A: A car in a dry, hot desert (low humidity). Scenario B: A car in a cool, foggy coastal city (high humidity).
Answer: Even though the desert is hotter, the coastal car will rust much faster. This is because rust requires water () as a catalyst. Without moisture, the oxidation reaction happens extremely slowly or not at all.
What is the scientific name for the process that creates rust?
Why is a burning match considered different from a rusting nail?
Painting a metal fence is done mainly for decoration and does not help prevent rust.
Review Tomorrow
Tomorrow morning, look around your house or school for something rusty. Can you explain to someone why that object changed color and what 'ingredients' caused it?
Practice Activity
Try the 'Penny Experiment': Place one copper penny in a dry jar and another in a jar with a damp paper towel. Observe them over three days to see which one changes color first!