An ion that does not participate in the overall reaction and is not affected by the change is a

• A. Catalyst
• B. Activation Energy
• C. Redox
• D. Spectator Ion

Answer: (D)

Spectator ions are ions that appear in solution but do not undergo any change during the reaction. They stay the same on both sides of the equation and don’t participate in bond-breaking or bond-making events, so they don’t affect the outcome of the reaction. They’re included to balance charge and mass in the full ionic equation but can be removed when forming the net ionic equation.

For example, in the reaction between silver nitrate and sodium chloride, silver and chloride form solid silver chloride, while sodium and nitrate remain dissolved as Na+ and NO3−. Those two ions don’t participate in the actual chemical change, so they’re spectator ions.

This idea distinguishes from a catalyst, which participates in the mechanism of the reaction and is regenerated, and from activation energy, which is the energy barrier to reaction, or from redox processes, which involve electron transfer.