Welcome to Catalysts and Enzymes!
In Chemistry, some reactions are naturally very slow. If we want to make products quickly—whether in a lab or in a massive factory—we need a way to speed things up without constantly adding more heat or pressure. This is where catalysts and enzymes come in. Think of them as the "fast-forward" buttons for chemical reactions!
What is a Catalyst?
A catalyst is a substance that increases the rate of a chemical reaction without being chemically changed or used up by the end of the reaction.
Because catalysts aren't used up, you only need a very small amount of them. They can be used over and over again. In a chemical equation, you won't see the catalyst written as a reactant or a product because it stays the same from start to finish.
Did you know? Catalysts are vital in industry. They allow companies to make products faster and at lower temperatures, which saves a huge amount of money and energy!
How Do Catalysts Work?
To understand catalysts, we need to remember Activation Energy (\(E_a\)). This is the minimum amount of energy that particles must have when they collide in order to react.
Imagine you are trying to push a heavy shopping trolley over a steep hill. If the hill is too high, you might not have enough energy to get to the other side. A catalyst is like finding a different path around the side of the hill that is much flatter and easier to walk.
In chemistry terms, a catalyst works by:
1. Providing an alternative pathway for the reaction.
2. This alternative pathway has a lower activation energy (\(E_a\)).
Because the "energy barrier" is lower, a higher proportion of collisions between particles will have enough energy to result in a reaction. This means there are more frequent successful collisions, which increases the rate of reaction.
Reaction Profiles
A reaction profile is a diagram that shows the energy changes during a chemical reaction. When you add a catalyst, the shape of the graph changes.
On a reaction profile diagram:
- The reactants are on the left and the products are on the right.
- The "hump" represents the activation energy.
- When a catalyst is used, the peak of the hump is lower than the original reaction.
- Important note: The energy level of the reactants and the products stays exactly the same; only the "hump" in the middle changes.
Quick Tip: If you are asked to draw this in an exam, always label the two different curves. Label the high curve as "uncatalysed" and the lower curve as "catalysed".
Enzymes: Nature's Catalysts
Enzymes are biological catalysts. They are large protein molecules that speed up chemical reactions inside living things.
While a normal chemical catalyst (like iron or platinum) might work on many different reactions, enzymes are usually very specific. This means one type of enzyme usually only speeds up one specific reaction.
Example: Fermentation
In Topic 9, you learn about yeast. Yeast contains enzymes that act as catalysts to turn sugar into ethanol (alcohol) and carbon dioxide. This process is called fermentation. Without the enzymes in the yeast, this process would be far too slow to be useful!
Don't worry if this seems tricky: Just remember that all enzymes are catalysts, but not all catalysts are enzymes. Enzymes are simply the version found in living organisms.
Quick Review & Key Takeaways
Check your understanding with these key points:
- Catalysts speed up reactions but are not used up themselves.
- They work by providing an alternative pathway with a lower activation energy.
- On a reaction profile, a catalyst lowers the "energy hill."
- Enzymes are biological catalysts (like the yeast used in fermentation).
- Catalysts increase the frequency of successful collisions.
Common Mistake to Avoid:
Students often say that catalysts "give particles more energy." This is not true! The particles have the same amount of energy as before. Instead, the catalyst lowers the requirement (the activation energy) needed for a successful collision. It makes the "target" easier to hit, it doesn't make the "ball" move faster.
Note: For more information on how temperature and concentration affect rates, see the chapter on "Collision theory and factors affecting rate". For more on energy changes, see "Exothermic and endothermic changes".