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This method is most useful when there are only two reactants. One reactant (A) is chosen, and the balanced chemical equation is used to determine the amount of the other reactant (B) necessary to react with A. If the amount of B actually present exceeds the amount required, then B is in excess and A is the limiting reagent.
Conversion and its related terms yield and selectivity are important terms in chemical reaction engineering.They are described as ratios of how much of a reactant has reacted (X — conversion, normally between zero and one), how much of a desired product was formed (Y — yield, normally also between zero and one) and how much desired product was formed in ratio to the undesired product(s) (S ...
r is the stoichiometric ratio of reactants, the excess reactant is conventionally the denominator so that r < 1. If neither monomer is in excess, then r = 1 and the equation reduces to the equimolar case above. The effect of the excess reactant is to reduce the degree of polymerization for a given value of p.
Stoichiometric equations are used to determine the limiting reagent or reactant—the reactant that is completely consumed in a reaction. The limiting reagent determines the theoretical yield—the relative quantity of moles of reactants and the product formed in a chemical reaction. Other reactants are said to be present in excess.
An excess reactant is a reactant that is left over once the reaction has stopped due to the limiting reactant being exhausted. Consider the equation of roasting lead(II) sulfide (PbS) in oxygen ( O 2 ) to produce lead(II) oxide (PbO) and sulfur dioxide ( SO 2 ):
and, assuming a one-to-one reaction stoichiometry, that excess of one substrate over the other is quantitatively preserved over the course of the entire reaction such that: [3] [B] t = [A] t + e. A similar set can be constructed for reactions with higher order stoichiometry in which case the excess varies predictably over the course of the ...
Animation of a strong acid–strong base neutralization titration (using phenolphthalein).The equivalence point is marked in red. In chemistry, neutralization or neutralisation (see spelling differences) is a chemical reaction in which acid and a base react with an equivalent quantity of each other.
In an ideal chemical process, the amount of starting materials or reactants equals the amount of all products generated and no atom is lost. However, in most processes, some of the consumed reactant atoms do not become part of the products, but remain as unreacted reactants, or are lost in some side reactions.