Chemistry · Reactivity 2: How much, how fast and how far?. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
A balanced equation is a recipe in moles. The coefficients give the mole ratio in which substances react and form. Every calculation follows the same path: change what you are given into moles, use the ratio, then change moles into the mass, gas volume or concentration you want.
Reactants are rarely mixed in the exact ratio. The limiting reactant runs out first and decides how much product can form. The other reactant is in excess.
The theoretical yield is the maximum amount the equation allows. Percentage yield compares what you actually obtained with it. Atom economy is different: it shows how much of the mass of the reactants ends up in the product you want.
Students choose the reactant with the smaller mass or the smaller number of moles as the limiting reactant. You must compare moles with the ratio in the equation before you decide.
Answer: 1.14 dm3 of hydrogen (HCl is the limiting reactant)
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