Navigation
Explore how physical form and special substances called catalysts influence chemical reactivity.
Why does a single giant log take hours to catch fire, while a handful of tiny wood shavings can start a blaze in seconds?
Chemical reactions happen when particles collide with enough energy. This is called Collision Theory. For a solid to react with a liquid or gas, the particles can only meet at the surface. If you have one large lump, the particles inside are 'trapped' and cannot react until the outer layers are gone. By crushing a solid into a powder, you increase the surface area, exposing millions of more particles to the other reactant simultaneously. More exposed particles lead to a higher frequency of collisions, which directly increases the rate of reaction.
Imagine you have two identical antacid tablets and two beakers of water. 1. Drop the first tablet into Beaker A whole. 2. Crush the second tablet into a fine powder and drop it into Beaker B. 3. Result: Beaker B fizzes violently and finishes in 10 seconds, while Beaker A bubbles slowly for 2 minutes. Even though the mass is the same, the powder has a much higher surface area-to-volume ratio.
Quick Check
If you double the surface area of a reactant, what happens to the frequency of particle collisions?
Answer
The frequency of collisions increases, which speeds up the reaction rate.
Sometimes, increasing surface area isn't enough. Enter the catalyst. A catalyst is a substance that increases the rate of a chemical reaction without being consumed or permanently changed. It works by providing an alternative reaction pathway. This new path has a lower activation energy (), which is the minimum energy required for a reaction to occur. Think of it like a tunnel through a mountain; instead of the particles needing massive energy to climb over the peak, they can take the 'shortcut' through the tunnel with much less effort.
Quick Check
True or False: A catalyst is considered a 'reactant' in a chemical equation.
Answer
False. It is not consumed by the reaction and remains unchanged at the end.
Catalysts aren't just for lab beakers; they are essential for life and technology. Enzymes are biological catalysts made of proteins. For example, amylase in your saliva breaks down complex starches into simple sugars almost instantly. In industry, catalytic converters in car exhaust systems use precious metals like Platinum () and Palladium () to convert toxic gases like Carbon Monoxide () into less harmful Carbon Dioxide (). Without these catalysts, our bodies couldn't function, and our air would be significantly more polluted.
Consider a single cube with a side length of . 1. Total Surface Area () = . 2. If we cut this cube into 8 smaller cubes (each with side length ): 3. of one small cube = . 4. Total for 8 cubes = . By simply cutting the object in half along three planes, we have doubled the surface area available for reaction while keeping the volume constant.
Which of the following would react the fastest with Hydrochloric Acid?
How does a catalyst change the activation energy () of a reaction?
Enzymes are biological catalysts that help speed up chemical reactions in the body.
Review Tomorrow
In 24 hours, try to sketch a reaction energy profile diagram showing the difference between a catalyzed and uncatalyzed reaction.
Practice Activity
Look at the ingredients on a box of laundry detergent or a bottle of contact lens cleaner. Can you find any ingredients ending in '-ase'? These are enzymes acting as catalysts!