I’ve asked this question to multiple teachers and googled it multiple times only to hear “yeah if you put a catalyst in a chemical it reacts faster” but I want to know what the catalyst actually does to do this
In: Chemistry
Catalysts lower the activation energy for the reaction pathway, resulting in an increase in the rate of reaction
They are somewhat like tools. Imagine trying to losen a screw without a screwdriver. It might be possible, but much more effective with the tool. For example enzymatic catalysis: a molecule that gets trapped in the enzyme might be “stretched” by electrostatic forces, which makes it easier for other molecules to interact with it. The stretch-mechanism might be so strong, that it even tears the molecule appart. Similar reactions occur in activated carbon for example.
Other kinds of catalysts can help reactions by making it easier to react by transforming one of the agents first, e.g. acids/bases that modify protons for easier access.
There are many ways to assist in a reaction, the gist of it is lowering the energy needed to get something done.
The example that is often used is burning wood.
Imagine a pile of fire wood. If you add sufficient heat, the wood will begin to burn, and then keep burning until it is all turned into ash and smoke. However, in order to start that reaction, you have to raise the temperature of the wood quite high, you have to overcome its activation energy. **A catalyst reduces the energy of activation**, allowing the reaction to proceed faster, sort of like putting gasoline on the wood. Now instead of needing to get the wood to a high temperature, you only need to get it hot enough to ignite the gas, which will then ignite the wood.
There are many types of catalysts, but generally, the catalyst will react with the reactant(s) in such a way that it “destabilizes” them and makes them more likely to react with each other. Molecules that are destabilized require less energy to react (in other words, this lowers the activation energy).
Here is a very basic catalysis:
https://www.chemistrysteps.com/acid-catalyzed-hydration-of-alkenes-practice-problems/#:~:text=Acid%2DCatalyzed%20hydration%20is%20the,cannot%20protonate%20the%20double%20bond.
The acid is sufficiently reactive to attack the double bond, which then causes the formation of a more reactive (i.e., less stable) carbocation. This carbocation is then able to participate in the desired reaction. At the end, the H+ is regenerated, so you have your catalyst back. It’s worth noting that this is not the same H+ that started the reaction, but because you started with an H+ and finish with an H+, it’s considered to be the catalyst of the reaction.
Often mentioned here but unfortunately not quite right: the catalyst doesn’t reduce the activation energy.
Image you are in a valley and want to commute to a nearby valley. To do that you have to climb the mountain first and then you can descend to your destination.
Now image you see another way to get to the same destination but along another way. This way may be a little bit long because you climb a different mountain, but this mountain is way way smaller.
That’s what the catalyst does: it opens a different way for the reaction to go along.
In this picture the height of the mountain stands for the activation energy. You must overcome it to progress to your products.
And now you can also see where the confusion about lowering the activation energy comes from: if you have a look from outside it *seems* as the activation energy is lower. But in reality the reaction process along a complete different reaction path.
Imagine iron rusting. You probably think of water, right?
Water is not involved in the chemical reaction of rust at all. Rust is when you take Fe and add some oxygen to make it Fe2O3. There’s no water molecules here. We’re not stripping oxygen from water and producing rust + hydrogen gas.
What happens is the water allows the oxidation process to occur more easily. I don’t know the exact mechanism, but maybe the oxygen dissolved in water has an easier time bonding to Fe than oxygen in the air. Perhaps the water is dissolving a bit of Fe from the surface and making a small galvanic cell.
It’s even possible that water is involved somewhere in the intermediate chemical reaction, for example:
O + H2O = 2 OH
2 Fe + 3 OH = Fe2(OH)3
Fe2(OH)3 +3 OH =Fe2O3 +3 H2O
It’s possible that the above sequence is easier than the simple 2Fe + 3O= Fe2O3.
So even if the catalyst is “used” it’s also produced, so in the end you have the exact same amount as you started. You lose Fe and O as rust is produced, but no water disappears.
Have you ever seen videos of people putting things together in a factory or something, and they have a jig to make sure the parts are lined up? You could have put the parts together with just your hands, but they’d be all over the room and in random orientations, so it would take longer to get them to fit. If you slot them into this jig, they’ll be lined up perfectly and it’ll take you less energy to add the glue or the screws or whatever completes the assembly. When you remove the completed article, the jig is not used up and can help speed up the next one.
Enzymes in particular are designed to have just the right shape to receive the two components of a reaction that would have been floating around randomly and unlikely to react (or one component to be split up). You slot the pieces in, they get joined while they’re in the right orientation, then they get released and the enzyme is ready to receive another one.
People have described catalysts that react with other reactants. There are also catalysts that just facilitate the reaction in other way.
For example in molecular clouds in outer space, lots of chemical reaction happen at the surface of grains of ice (mostly water ice), because molecules and atoms that stick to the surface of those grains are more likely to meet each other and react.
Thankyou for all the answers, they make so much more sense!
I now understand that catalysts aren’t all the same mechanism and work in different ways, simply making a specific reaction easier
A molecule having an element in it loosely connected can be a catalyst because the same element in another molecule has a much stronger bond would require significantly more energy, while that first molecule can take the element back from the reaction and was just used to crack the other molecule (or something along those lines, I haven’t done chemistry since high school lol)
The example is was taught in school was in electrolysis a slab of carbon at the bottom of the tank makes the reaction easier and for the rest of my life I always just assumed a catalyst just sits there and magic makes it work easier
In chemistry if you drew a graph of all the energy in a chemical reaction you would see a flat line, parabola that goes up and then down, and then a slope down to another flat line at a lower energy.
In order to raise the energy in the system often some sort of heat or energy needs to be added into the chemical system, this added energy is called the activation energy.
What a catalyst does lower this activation energy.
Think of when you open a bottle of soda at first you open the bottle and bubbles form, you had to put in some energy to get the cap off and you have a reaction, well if you then take a mentos mint and put it in there, suddenly the energy needed for the reaction is reduced and lots of bubbles form. In this case the mentos doesn’t react chemically it reacts physically it is not used up in the reaction and so in this case the mentos is a catalyst. Its not a perfect example since the activation energy in this case is twisting the cap off and that will stay the same regardless but I think it shows what a catalyst does.
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