In anatomy, the second cervical vertebra of the spine is named the axis or epistropheus. By the atlanto-axial joint, it forms the pivot upon which the first cervical vertebra, which carries the head, rotates. The most distinctive characteristic of this bone is the strong odontoid process known as the dens which rises perpendicularly from the upper surface of the body. That peculiar feature gives to the vertebra a rarely used third name: vertebra dentata. In some judicial hangings the odontoid pr
1 An acid-base reaction is type of double displacement reaction that occurs between an acid and a base. 2  The H + ion in the acid reacts with the OH-ion in the base to form water and an ionic salt: 3  HA + BOH â H 2 O + BA. 4  The reaction between hydrobromic acid (HBr) and sodium hydroxide is an example of an acid-base reaction: Direct Combination or Synthesis Reaction. 2  In a synthesis reaction two or more chemical species combine to form a more complex product. 3  A + B â AB. 4  The combination of iron and sulfur to form iron (II) sulfide is an example of a synthesis reaction :
A chemical reaction is usually accompanied by easily observed physical effects, such as the emission of heat and light, the formation of a precipitate, the evolution of gas, or a color change.