Catalysts and chemical reactions

[Weyoun]

Hi there

While I understand the concept of catalysts and their role in reactions (reduction of the activation energy, increases the rate of reaction), I don't quite get how scientists were able to conclude that particular compounds could form more effective catalysts than others. Leaving surface area aside, what are the actual chemical/atomic properties of a catalyst that allow it to both reduce the activation energy and increase the rate of reaction? Were these compounds simply selected from trial and error?

I just began reading a page about the transition state theory. Personally, I'm way more comfortable with atomic explanations of chemical phenomena than simple analogies and memorising, so if someone could explain to me exactly what the 'activation energy' of a reaction is, that would be great. Must the particles or polyatomic ions of a reaction be in a state of higher-energy 'flux' before being allowed to form additional bonds? Why exactly does a catalyst reduce this value? I can see that if this were true, then we would see a corresponding increase in the reaction rate, as the system would already be in a high-energy state without the addition of high temperatures.

On the other hand, if someone could point me in the direction of some quality additional reading, it would be much appreciated.

While I'm only a simple Australian High School student and haven't learnt much atomic theory regarding chemistry, I'd love to have a greater understanding of the exact concepts.

Thanks for your time

 

[rgwalt]

A catalyst lowers the activation energy of a reaction by providing an alternate path for the reaction to take. You can think of a catalyst as providing sites for molecules or atoms to temporarly assosiate with. These site associations allow reactants to react as they are in close vicinity to each other.

Elements of Chemical Reaction Engineering by Fogler is a good beginners book on reaction engineering and catalysis. It is a college level textbook though, and will require that you understand differential and integral calculus.

Ryan

 

[jwo7777777]

Catalysts are just cheap hourly hotels for chemicals to get it on.

 

[zzzz]

Physical Chemistry by Atkins

 

[Mday]

some discoveries are accidental, some are theorized through analyses to be catalysts, then tested...

it's important to know that catalysts are used to "speed up" the process of reactions by lowering the required activation energy. They are not intended to cause reactions which will never happen in certain conditions (entropy). The speeding up of rates can be as extreme as a reaction which takes hundreds of years down to as little as a few minutes, some exaggeration exists with these numbers of course...

all things want to be at the least possible energy state they can be in. This is why some things rust and corrode, and why chemical reactions happen (for the most part). A substance which is somewhat chemically unstable, like hydrogen peroxide, will break down over time, by itself. 2 substances, when mixed, may find itself in a lower energy state if they chemically change, forming a 3rd, or 4th product. when a catalyst is introduced, there is a sequence of steps which are added in the breakdown or formation process which are fast due to the lower activation energy required. These sequence of FASTer steps replace some steps which are slower.

basically, the parts of a chemically unstable molecule have an afinity to parts of the catalysts than each other. or molecules of 2 substances have an affinity to attach itself to the catalysts, opening bonds which allow for the formation of a 3rd substance. affinity comes from the fact that substances want to be at the lowest energy states...

 

[sao123]

Understand this....
many reactions dont occur without other intermediate ingredients and steps.

Many catalysts can assist a reaction by providing a better means for splitting molecules and rejoining the atoms in different ways.
Certain catalysts split molecules better than others. Certain catalysts join molecules better than others. It all depends on what atoms or groups of atoms react well together.

 

[Shalmanese]

Well, there are many different ways a catalyst can aid reactions but I'm assuming you are only learning one of them (god bless the planned ignorance model of the Australian High School system )

Its a long time since I did this so excuse me if I make any serious blunders.

Hetrogeneous cats are usually solids and basically just provide a place for the reaction to occur (eg. the cat converter in a car made of platinum/irridium).

Homogenour cats temporarily bond with the chemical to form an intermediate step but then unbond to form the final product. Basically, if you have a reaction AB + CD -> A + B + C + D -> AC + BD, AB may only split if the activation energy is high enough. if you have a cat, it goes AB + CD + Cat -> ACat + B + C + D -> AC + BD + Cat. the presence of a cat means that it takes less energy for AB to split.