By Jack Brubaker | Updated Aug 30, 2022
Chemistry students often find it challenging to predict reaction products. With systematic practice, the process becomes intuitive and reliable.
Identifying the reaction type—displacement, acid‑base, or combustion—is usually the first hurdle. Each type has distinct, recognizable signatures:
Determine the cation and anion of each reactant and note their charges. Reference a cation–anion table (e.g., Penn State University) if needed.
Exchange the anions between the two reactants. The general format is:
AB + CD → AD + CB
Example: NaCl + AgNO₃ → NaNO₃ + AgCl
Check each product against solubility rules (e.g., Southern Methodist University). NaNO₃ is soluble; AgCl is insoluble and will precipitate.
Confirm that each atom appears on both sides. In the example, the counts are already equal, so the equation is balanced.
Locate the acidic species (contains H) and the basic species (typically an OH⁻ salt).
acid + base → salt + water
Example: HCl + NaOH → NaCl + H₂O
Use solubility rules to confirm that the resulting salt remains in solution.
In this instance, the equation is already balanced.
The fuel supplies C/H; the oxidant supplies O₂. In air, O₂ is the default oxidant, though alternative oxidants like N₂O can be used under special conditions.
Assume the standard outcome:
Fuel + O₂ → CO₂ + H₂O
Example with propane: C₃H₈ + O₂ → CO₂ + H₂O
For propane: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
