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It depends on the chemical reaction but remember to convert to moles and find the amount each reactant makes of a specific product. Compare the amounts made by the two reactants and the one that makes less of the same product is the limiting reactant. There can be more than one limiting reactant but that would both reactants that are limiting create the same amount of one product and are both used up in the reaction.
In theory, there can be two limiting reactants if two reactants are present in the exact amounts necessary to use up both reactants. However, in practice, it's extremely unlikely that two reactants are present in the exact same amounts, so there is only one limiting reactant. For example, if two reactants are used at the same rate and it is measured that there are 2.50 grams of both reactants, it will almost always be the case that one reactant will still be present in a very slightly larger/smaller amount. This means that one of the reactants will be left over, but the instruments we use are not accurate enough to see it. Even if the difference is extremely small, we still consider the one that is present in the smaller amount the limiting reactant, so there will only be one limiting reactant.
A little unrelated, but if there is a reaction that requires a catalyst, and the catalyst is present in very small quantities relative to the reactants, is it called a limiting reactant because it severely slows the reaction, or do we classify it as something else?
andrewcj 4I wrote:A little unrelated, but if there is a reaction that requires a catalyst, and the catalyst is present in very small quantities relative to the reactants, is it called a limiting reactant because it severely slows the reaction, or do we classify it as something else?
The catalyst is not a limiting reactant because the reaction occurs independently with or without the presence of a catalyst.
I don't believe that there can be more than one limiting reactant. In a reaction, there is ONE limiting reaction and the others are in excess. Once the limiting reactant is used up, the reaction can no longer occur, because the amount of product being produced is limited.
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