Chemical equations and units

Chemical reactions are summarised by writing a chemical equation. By convention the reactants are on the left-hand side and the products are written on the right-hand side in the following format  

Some reactions can proceed in either direction and it is not then possible to specify the products or the reactants uniquely. These are written  

Chemical equations are devices for accounting . In the course of chemical reactions, no atoms must be lost or gained. Chemical equations should therefore be balanced to ensure that this rule holds. Typical balanced equations are  

Sometimes it is desirable to specify the state of the reactants, whether solid, liquid or gas, or in solution. In such cases a symbol enclosed in brackets after the species gives this data s = solid  

1 = liquid g = gas aq = water (aqueous) solution. These are only labels and are not a part of the reaction. For example  

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