And pure substances, because they don't have concentrations, aren't included in equilibrium calculations.

这就是为什么水既可以显酸性也可以显碱性。

And so just to get our terminology, we call these different substances-- these pure substances that have these specific properties at certain temperatures and react in certain ways-- we call them elements.

因此，为了获得我们的术语，我们称这些不同的物质——这些在特定温度下具有这些特定性质并以特定方式发生反应的纯物质——我们称它们为元素。