Final answer:
Chemical substances in different forms impact how they affect the body, and there are standard conditions like the standard state used for consistently reporting thermodynamic properties such as the standard enthalpies of formation.
Step-by-step explanation:
Chemical substances can exist in several forms including solids, liquids, gases, fumes, mists, and vapours, and the state of a substance greatly influences how it interacts with the body and the potential harm it can cause. The standard conditions for reporting thermodynamic properties include the standard state where substances are measured at a pressure of 1 atmosphere and for solutions, a concentration of 1 molar, usually at 298.15 K (25°C). These conditions are used to ensure consistency in reporting and comparing data such as standard enthalpies of formation (AH), which is the enthalpy change when 1 mol of a compound is formed from its component elements in their standard states.