Читать книгу The Handy Chemistry Answer Book - Justin P. Lomont - Страница 27

How can we make chemical reactions go faster?

Two of the most common ways to make a reaction proceed faster are to increase the temperature at which the reaction is carried out or to use a catalyst to lower the energetic barrier to the reaction. With increased temperature, the amount of thermal energy available to overcome the energetic barrier to the reaction is increased. Of course, you’ll also get more products faster if you just increase the concentration(s) of the reactant(s). Light can also serve as the catalyst, breaking a chemical bond to produce a species that is more reactive that the original reactant species.

Plants like this one combine nitrogen and hydrogen using the Haber-Bosch process to manufacture ammonia.

What is a catalyst for a reaction?

A catalyst for a chemical reaction is any chemical species that lowers the amount of free energy necessary to achieve the chemical transformation. This may involve a significant change in the mechanism by which the reaction takes place. Light may also serve as the catalyst.

What are some industrial processes that make use of catalysts?

The chemical industry uses catalysts in a staggering array of chemical reactions that make products that we all use every day. The production of ammonia (NH₃) from nitrogen (N₂) and hydrogen (H₂), known as the Haber-Bosch process, uses iron or ruthenium catalysts; this reaction is used to generate about five hundred million tons of fertilizer per year! Most of the world’s plastic is made by one form of catalysis or another, and the refining of crude oil into gasoline and other fuels is also possible because of catalysts. Catalysts are also used in food processing and production—margarine is made by reacting fats with hydrogen gas in the presence of a nickel catalyst.

What chemicals are produced on the largest scale?

In terms of volume (not profit), sulfuric acid is the largest chemical produced worldwide. Global consumption is around two hundred million tons per year—a number that is just too impossibly large to imagine. Nitrogen (N₂), ethylene (CH₂CH₂), oxygen (O₂), lime (mainly CaO), and ammonia (NH₃) round out the top five, though sometimes these change.

What is the difference between heterogeneous catalysis and homogeneous catalysis?

Homogeneous catalysis takes place when the catalyst and the other reactants are all dissolved in the same solution. Heterogeneous catalysis typically involves the use of a catalyst that is insoluble, or perhaps only weakly soluble, in the solution in which the reaction takes place. Thus, in heterogeneous catalysis, the catalyst and solution may form a suspension, or the catalyst may simply be a solid that is placed in the solution.