By Grant D. McKenzie • Updated Aug 30, 2022

Chemistry students routinely use skeleton equations as a foundational tool for balancing reactions. The reactants are written on the left side, the products on the right, and an arrow connects them, giving the equation its “skeleton” structure. Completing the equation requires determining the correct stoichiometric coefficients, which indicate the relative amounts of each species.

Step 1: List the Reactants

Identify all reactants and place them on the left‑hand side, separated by plus signs. Follow the reactants with a reaction arrow. For example, if calcium chloride and sodium sulfate are reacting, write:

CaCl₂ + Na₂SO₄ →

Step 2: Write the Products

Place the corresponding products on the right side of the arrow, again separated by plus signs. In the example above, the products are calcium sulfate and sodium chloride:

CaCl₂ + Na₂SO₄ → CaSO₄ + NaCl

At this stage the equation is still a skeleton, as the numbers of sodium and chlorine atoms do not match on both sides.

Step 3: Add State Symbols

State symbols clarify the physical conditions of each compound—solid (s), liquid (l), gas (g), or aqueous solution (aq). In our example, two aqueous solutions combine to form an aqueous solution and a solid precipitate:

CaCl₂ (aq) + Na₂SO₄ (aq) → CaSO₄ (s) + NaCl (aq)

With the state symbols in place, the skeleton equation is ready for coefficient balancing, ensuring mass conservation across the reaction.

These steps provide a clear framework for constructing skeleton equations before applying algebraic methods to balance them.