ABSTRACT
This chapter explores changes studied in chemistry, especially chemical reactions. The ideal gas law only approximately applies to real gases and for more precise work another more detailed model needs to be used that allows for the modest level of transient ‘proto-bonding’ between the gas molecules. There is a rule-of-thumb that physical changes require less energy than chemical changes, which involve the breaking and making of strong chemical bonding. Chemistry is the science that studies the properties of different substances and, in particular, their chemical properties: which substances react with which other substances, under what conditions, and what new substances are produced. The chemical literature reports a vast number of chemical reactions. Chemists refer to ‘types of reactions’ as part of a strategy to organise vast amounts of data. Classes of reaction do not generally refer to reactions of specific substances but to classes of substance.
