Other conditions for chemical processes

Other factors also affect the reactions process. The solidifying process of chalk (CaCO3) is an example:

Note that solidifying is reduced at lower temperatures; and a higher concentration of carbon dioxide accelerates the chemical reaction, even if not all of it is used in the reaction or is part of the final product.

The size of the particles also plays a role: the finer the particles, the greater the surface of the materials, making the reaction quicker. Finely ground cements, for example, have a shorter setting time. In a few chemical reactions with gases, air pressure plays an important role - pressure decides the weight of the gases.

In chemistry there are also catalysts, which increase the rate of the reaction without actually 'chemically' taking part in it. In an animal's digestion system catalysts are known as vitamins and play a vital role in a whole series of processes. Catalysts play an important part in many industrial processes.

A chemical reaction can, in principle, be reversed, and must be seen as a reaction in equilibrium. Chemical compounds can be stable, meta-stable and unstable. Life would not have been possible without meta-stable systems.

4.1.5 The elements

Ninety-nine per cent of the Earth's crust consists of ten elements. The other 1% consists of, amongst other elements, carbon, which is a condition for biological processes.

There is a difference between organic and inorganic compounds. Carbon is the basic element in all life, and is present in all organic

Table 4.2 The most common elements

Element

Chemical symbol

Per cent of Earth's crust

Oxygen

O

49.4

Silicon

Si

25.8

Aluminium

Al

7.5

Iron

Fe

4.7

Calcium

Ca

3.4

Magnesium

Mg

1.9

Sodium

Na

2.6

Potassium

Ka

2.4

Hydrogen

H

0.9

Titanium

Ti

0.6

Total

99.2

compounds, including lifeless compounds such as oil and limestone that were originally created from decomposed living organisms.

There are 500 000 carbon compounds. They include many compounds not found in nature, including modern plastics. The inorganic compounds number approximately 80 000.

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