Читать книгу Foundations of Chemistry - Philippa B. Cranwell - Страница 45
0.7.3 Indicating the physical state of reactants and products in chemical equations
ОглавлениеWhen writing chemical equations, it is sometimes helpful to include the physical state of the reactants and products in the equation. This is especially important in equations relating to energy changes, as the energy required or released in the reaction depends upon the physical state of the products.
The common symbols used to describe the physical state of a reactant or product are given in Table 0.5.
Table 0.5 State symbols commonly used in chemical equations.
| Example | |||
|---|---|---|---|
| State | Symbol | Formula | Substance |
| Gas | g | H2O(g) | Water vapour or steam |
| Liquid | l | H2O(l) | Liquid water |
| Solid | s | H2O(s) | Ice |
| Solid1 | gr | C(gr) | Graphite |
| Solid1 | d | C(d) | Diamond |
| Aqueous2 | aq | NaCl(aq) | Sodium chloride dissolved in water |
1 The forms (called allotropes) of carbon, i.e. graphite and diamond, have specific symbols as energy changes are slightly different depending upon the form of carbon used in the reaction.
2 Aqueous means that the substance is dissolved in water or is in aqueous solution.
