Consider a chemical equation with two reactants forming one product. If you know the mass of eac

Consider a chemical equation with two reactants forming one...

Key Concepts

Molar Mass (Atomic Masses)

Molar mass, derived from the relative atomic masses of elements, is used to convert between the mass of a substance and the number of moles. Knowing the molar mass of each reactant and the product is crucial for applying stoichiometry properly, as it provides the bridge between measured masses and the mole ratios given in the balanced equation.

Balanced Chemical Equation

A balanced chemical equation not only shows the reactants and products involved in a reaction but also gives the stoichiometric coefficients that indicate the exact number of moles of each substance that participate. This information is essential to relate the masses of reactants to the masses of products, as the coefficients determine the proportion in which reactants combine and the product is formed.

Stoichiometry

Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. It allows you to convert between mass, moles, and number of particles using molar masses and the balanced chemical equation. With the masses of the reactants and the molar ratios provided by the equation, you can calculate how much product should be formed.

Limiting Reactant

The limiting reactant is the substance that is completely consumed first during a chemical reaction, thereby limiting the amount of product that can be formed. Even if you know the masses of both reactants, you must identify which one is limiting, because the mass of the product is determined solely by the quantity of the limiting reactant converted according to the stoichiometric ratios.

Transcript

00:01 For this question, i'll start with a generic reaction of a plus b goes to one product, c.

00:11 It states that if you know the mass of each reactant, what else do you need to know to determine the mass of product? well, to calculate the mass of product, you need to know the mass of each reactant and you need to know the stoichiometry of the reaction in addition to the molar mass of each reactant.

00:32 It is only with this information that you can determine the mass of the product.

00:40 What you would do is you would take the mass of each reactant, convert it into moles of each reactant, using the molar mass of each reactant, then go from moles of reactant to moles of product.

00:55 Whichever reactant produces the least amount of product, that then is your limiting reactant, and the maximum amount of product you can create will be the amount coming from the limiting reactant.

01:08 So the two additional pieces of information you need are the chemical reaction must be balanced so that you know the stoichiometry of the reaction, and you need to know the molar mass of each reactant in order to determine the limiting reactant.

01:31 The follow -up to this asks why the mass of c is simply not the sum of the mass of the two reactants.

01:38 It would only be the sum of the mass of the two reactants if both reactants were consumed completely and there was no limiting reactant.

01:47 This is based upon the law of conservation of mass.

01:52 If a and b are consumed completely in the process of making c, then c will be the sum of the masses of a and b.

02:00 However, if one of them, a or b, is not consumed completely because it is the limiting reactant, then we can't sum the masses of the reactants to get the sum of the masses of the products or the mass of the product if there's just one.

02:20 To provide a little bit more detail, it asks you to give a real example and support your answer mathematically.

02:29 So let me show you how this can be done.

02:33 Let's start with some generic reaction.

02:35 Well, let's start with the reaction.

02:39 2h2 plus o2 goes to two waters.

02:43 This means that two molecules of hydrogen react with one molecule of oxygen to make two molecules of water...

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