The Hill system (or Hill notation) is a system of writing empirical chemical formulas, molecular chemical formulas and components of a condensed formula such that the number of carbon atoms in a molecule is indicated first, the number of hydrogen atoms next, and then the number of all other chemical elements subsequently, in alphabetical order of the chemical symbols.
Iodine clock reaction. The iodine clock reaction (STd3) is a classical chemical clock demonstration experiment to display chemical kinetics in action; it was discovered by Hans Heinrich Landolt in 1886. Two colourless solutions are mixed and at first there is no visible reaction.
In the most known Landolt's clock reaction, potassium iodate and sulfite reacts with each other according to the clock mechanism to yield iodine, which than reacts with starch producing a dark blue colored complex. Various combinations of reactants that follow the clock mechanism are described in this section.