今天看到了一个很有意思的词spectator ions旁观离子，以前学化学的时候没有注意到。就像上图中的反应方程式，硝酸根和钠离子反应前后都没有发生变化，这个就是旁观离子。
A spectator ion is a charged atom or group of atoms in a chemical reaction that does not undergo a chemical change or change state when the reaction takes place. In chemical reactions, compounds that contain ions are often dissolved in water, resulting in a state called aqueous ions. When two ionic compounds are dissolved into an aqueous state, or both are dissolved into the same solvent, their ions separate, so any ions that made up the first compound can interact with any ions from the second compound. It is not necessary for all ions to interact in this state, and if some ions do not interact, they usually remain dissolved in solution.