What is a Catalyst?

Answer: A catalyst is a substance which changes the rate of a reaction without being used up by the reaction. 
This diagram explains the effect of a catalyst as lowering the activation energy needed for a reaction to occur. Source
A catalyst essentially lowers the amount of energy (called the activation energy) needed to run a chemical reaction. This will allow for more of this reaction to occur which will have the outcome of usually speeding up your entire experiment. There are two different types of catalysts:

Heterogeneous Catalysts- When the Catalyst is in a different phase when compared to the other reactants.

Homogeneous Catalysts- When the Catalyst is in the same phase when compared to the other reactants.

This paper describes an interesting use of catalysts, where the scientists formed Methane based on an Iron Catalyst and some CO2. Catalysts are used in many reactions where the activation energy is to high and prevents the reaction from occurring under normal circumstances.

How can I identify a Catalyst?

You will usually find a catalyst at the beginning (with the reactants) of a multi-step process and at the end (with the products). Then you can identify a substance as being a catalyst, since it was unchanged throughout the entire process.

A biological catalyst which breaks down maltose sugars into glucose. Source

What is a biological Catalyst called?

A biological catalyst is known as an enzyme, since these are materials are proteins which were molded so that they could help speed up reactions which take place inside of the cell. They do this by supporting or hindering reactions through their active sites, which allows cells to regulate the reactions inside of them. Inorganic molecules can also serve as catalysts in biological systems, but these are not unique to biological systems.

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