Occum's razor: William of Occum (1285?-?1349). If there are several possible explanations for some observation, and no significant evidence to judge the validity of those hypotheses, you should always use the simplest explanation possible. Occum's razor is also known as the principle of parsimony – scientists should make no more assumptions or assume no more causes than are absolutely necessary to explain their observations.
Open system: a reaction system in which matter can enter or exit. An open system can reach a steady state. The opposite of a closed system.
Oxidation: oxidation is one half of the oxidation-reduction process. In an oxidation, a substance has an increase in its oxidation number. In an oxidation a substance loses electrons. Thus the following is an oxidation half-reaction:
where the oxygen oxidizes from -2 to 0. It is not possible to carry out an oxidation without some other substance being reduced.
Oxidation number: is a method of keeping track of the movement of electrons in a chemical reaction, and are assigned using a set of internally consistent rules. When assigning these numbers remember that each atom has an oxidation number, as follows:
| Oxidation number | Example | |||
| 1. | Elements is 0 | In Cl2 each Cl atom = 0 | ||
| 2. | Monatomic ions is the ionic charge | Mg2+ = +2, Cl- = -1 | ||
| 3. | In compounds, oxygen atoms are usually -2. In peroxides, they are -1. | In H2O the O = -2, in H2O2 the O = -1 | ||
| 4. | In compounds, hydrogen atoms are usually +1, except in metal hydrides where they are -1. | In H2O each H atom = +1, in NaH the H atom is -1 | ||
| 5. | All other oxidation numbers are assigned so that the sum of all the oxidation numbers equals the ionic or molecular charge. | In Cr2O72- first assign O = -2. Then (2 x Cr) + (7 x -2) = -2, so each Cr atom = +6 |
Oxidizer: you cannot burn a fuel without an oxidizer. On earth, oxygen gas is the most common oxidizer, since it is present almost everywhere. In order to burn things rapidly requires a concentrated supply of oxygen. For example, in oxy-acetylene welding the gas is compressed in an oxygen cylinder. In spacecraft the oxidizer must be transported with the spaceship. Liquid oxygen is usually used in launching rockets from the Earth's surface. However, since it boils at -183 șC, it would be difficult to store for long term use. Better oxidizers for this purpose include dinitrogen tetroxide, which can be kept liquid without refrigeration.