How can you determine states of matter in a chemical equation?
It is not always possible.
The chemical reaction equation is a molar balance of the changes taking place. It does not specifically identify either the reaction conditions or the states of the materials, although they may be optionally referenced.
On the general assumption that unless otherwise specified , reactions are taking place at “normal temperature and pressure” we may be able to infer the states of matter from what we should know about the materials. If other conditions are stated, then again we may be able to look up the expected state of the material at those conditions.
Generally, a clear reaction equation will include the state of a compound with a parenthetical script: (s) – solid, (l) – liquid, (g) – gas. For example: