In the example, you must make it clear by adding the nature of the different substances in the reaction. In other words, if it is a solid, you need to put an “s” after the solid and an “aq” after substances that are in solution, in this case, aqueous refers to a solution in water specifically. In a neutralization reaction or acid-base reaction, an acid and base are mixed together. The acid, by definition, produces H+ or hydrogen ions. The base or alkaline substance produces OH- or hydroxide ions. These naturally produce water as an end product. The acid and base substances themselves will produce a type of salt. For example, sodium hydroxide (NaOH) and hydrochloric acid (HCl) make water and sodium chloride (NaCl). Water is also a natural end product. In a combustion reaction, a fuel reacts with an oxidizing agent (usually oxygen), with heat energy released. These are, by nature, exothermic. The energetic substance used in these types of reactions is usually a hydrocarbon, which involves carbon, oxygen, and hydrogen mainly. The end product is going to be CO2 and water.
LIMITING REAGENTS As mentioned, the limiting reagent or limiting reactant is the reactant that gets completely used up in a reaction, therefore determining when the reaction stops. It can be determined directly from knowing the number of grams of a reactant and knowing the molecular weight of the reactant. In any given reaction, there will often be one reactant that will have fewer “moles” than the other, making it the limiting reactant. The other will be the in-excess reactant. There are two approaches to determining the limiting reagent and amount of end product made, including the following: •
Approach 1: Find the balanced chemical equation and convert all the grams to moles in the reaction. Find out which reactant has fewer moles. Use this to determine the number of moles of product that can be made by the limiting reactant moles. Reconvert the end product back into the number of grams of end product that can be made. You can also calculate the grams of the in-excess reactant this way. 106
