Chemical Equations
chemical equation: a set of symbols that describe a chemical reaction. For example:
This equation states that 2 molecules of H2 (gas) and 1 molecule of O2 (gas) react to produce 2 molecules of H2O (liquid) and heat (energy).
reactants: the starting materials; chemicals (and things like energy) that react. In a chemical equation, the reactants are before the arrow (on the left).
products: chemicals (and other things like energy) that are produced. In a chemical equation, the products are after the arrow (on the right).
reaction conditions: anything that doesn’t take part in the reaction, but is needed to make the reaction happen. In a chemical equation, reaction condition information is placed above and/or below the arrow.
Symbols Used in Chemical Equations
The following symbols are commonly used in chemical equations:
|
Symbol |
Meaning |
|
(s) |
solid |
|
(ℓ) |
liquid (A script “L” is used to avoid confusion with the number 1.) |
|
(g) |
gas |
|
(↑) |
gas (formed by the reaction and not collected) |
|
(aq) |
aqueous (dissolved in water) |
|
(ppt) or (↓) |
solid (formed by the reaction) |
|
(cr) |
crystalline (solid is in the form of crystals, not powder or lump) |
|
Δ |
heat |
In the reaction:
the Δ means heat was needed to get the reaction started, even though it produced more heat once it got going.