Chemical equations use a language of symbols to explain what is happening in a chemical reaction. Each piece of a chemical equation is explained below.
First, here is a quick guide for interpreting chemical formulas. Highly recommended! One page, pretty easy to understand.
Chemical Element Symbols: each element has a one or two letter symbol; it always has exactly one capital letter.
3H2Se(g)
•Some symbols are based on old Latin names of elements; for example, tungsten’s symbol is “W”, because its Latin name is wolfram.
Coefficient: number of particles
Example: 3H2Se(g)
•The above example represents three molecules of H2Se (H2Se is a molecule, and molecules are particles).
•If no coefficient is listed, the coefficient is one.
•Coefficients can describe number of atoms OR molecules.
Examples: “2Ca” means two calcium atoms, and “3CO2” means three CO2 molecules. We can tell that CO2 is a molecule, because there is more than one atom.
•Coefficients in chemical equations work the same way they do in algebra – they multiply everything in that term. Terms (substances) are separated by “+” or “
” symbols.
Subscript: number of atoms in the molecule
Example: 3H2Se(g)
•Subscripts are small, lowered numbers.
•If no subscript is listed, the subscript is one.
•The subscript comes after its element symbol.
•In the example, each atom of H2Se has two atoms of H.
•3H2Se has six atoms of H and three atoms of Se: the coefficient multiplies each subscript (3 x 2 = 6 H and 3 x 1 = 3 Se)
State: the state of matter of the substance.
Example: 3H2Se(g)
•The states are solid (s), liquid (l), gas (g), and aqueous (aq).
•Aqueous means the substance is dissolved in water.
•You get aqueous NaCl (salt) if you dissolve it in water – the water breaks the solid down to individual particles that seem to disappear into the solution. To get liquid NaCl, you’d have to heat your salt to about 1500°F and melt it. Big difference.
“+” sign:
This sign means “and” or “reacts with” if you’re making a sentence. Different substances are separated by “+” in an equation.
•There’s a big difference between “W + C” and “WC.” When “WC” is written together with no “+” sign, the two elements are bonded together as a compound. “W+C” means it is a mixture of separate, unbonded W and C atoms. “W, “C”, and “WC” are three completely different substances with completely different properties.
“” Reaction Arrow
The reaction arrow separates the reactants from the products. If you’re making a sentence from a chemical equation, you can substitute the words “reacts to form” for the arrow.
Reactants → Products
Reactants: the starting substances or ingredients in a reaction. Found on the left side of a chemical equation.
Products: the ending substances or final results in a reaction. Found on the right side of a chemical equation.