What is the Limiting Reagent?
It is simply the substance in a chemical reaction that runs out first. It seems to simple, but it does cause people problems. Let’s try a simple example. Reactant A is a test tube. I have 20 of them. Reactant B is a stopper. I have 30 of them. Product C is a stoppered test tube. The reaction is: A + B —> C or: test tube plus stopper gives stoppered test tube. So now we let them “react.” The first stopper goes in, the second goes in and so on. Step by step we use up stoppers and test tubes (the amounts go down) and make stoppered test tubes (the amount goes up). Suddently, we run out of one of the “reactants.” Which one? That’s right. We run out of test tubes first. Seems obvious, doesn’t it? We had 20 test tubes, but we had 30 stoppers. So when the test tubes are used up, we have 10 stoppers sitting there unused. And we also have 20 test tubes with stoppers firmly inserted. So, which “reactant” is limiting and which is in excess? An Exercise in Limiting Reagent Here is what you know
