Consider the following balanced chemical equation: A 1 5B h 3C 1 4D a. Equal masses of A and B are reacted. Complete each of the following with either “A is the limiting reactant because ________”; “B is the limiting reactant because ________”; or “we cannot determine the limiting reactant because ________.” i. If the molar mass of A is greater than the molar mass of B, then ii. If the molar mass of B is greater than the molar mass of A, then b. The products of the reaction are carbon dioxide (C) and water (D). Compound A has a similar molar mass to carbon dioxide. Compound B is a diatomic molecule. Identify compound B, and support your answer. c. Compound A is a hydrocarbon that is 81.71% carbon by mass. Determine its empirical and molecular formulas

Understanding a balanced chemical equation is essential in the study of chemistry. It represents a chemical reaction where the number of atoms for each element is the same on both the reactant and product sides. Balancing an equation ensures the law of conservation of mass is followed; mass can neither be created nor destroyed in a chemical reaction.

To identify the limiting reactant from a balanced chemical equation, you would first take into account the stoichiometry, which tells you the ratio in which the reactants combine. In our exercise, A reacts with B in a 1:5 ratio. This ratio is based on the balanced equation and is used along with the molar masses and the amounts of each reactant to determine which one is the limiting reactant—that is, the reactant that will be entirely consumed first, stopping the reaction.

Example of Identifying Limiting Reactant

If you're given equal masses of two reactants, as in the exercise, the reactant with the greater molar mass will have fewer moles present. Since the reaction occurs at a fixed ratio, fewer moles mean that reactant will limit the extent of the reaction and is thus the limiting reactant. It's like making sandwiches: if you have the same weight in bread (A) as you do in cheese slices (B), but each slice of bread is heavier than each cheese slice, you will run out of bread first, making it the limiting 'reactant' for your sandwich production.

Molar mass is the weight of one mole (6.022 x 10²³ particles) of a substance and is expressed in grams per mole (g/mol). This concept is crucial when dealing with chemical reactions because it allows us to convert between mass and moles, an essential step in stoichiometric calculations.

To find how many moles of a substance you have, divide the mass of the substance by its molar mass. This is demonstrated in the textbook exercise where the molar mass determines the moles of each reactant available from a given mass, which in turn dictates the limiting reactant. Knowing that equal masses of A and B are used, the molar mass informs us which reactant is in short supply quantitatively.

Understanding Molar Mass in Calculations

Molar mass also helps in identifying substances in a reaction. For instance, if compound A has a molar mass close to that of carbon dioxide, knowing the molar mass of CO₂ enables us to infer possible formulas for compound A. Molar mass is a gateway to understanding the proportions and conversions between atoms and molecules in a chemical equation.

The empirical formula represents the simplest whole-number ratio of elements in a compound, while the molecular formula is the actual number of atoms of each element in a molecule of the compound. While the empirical formula is foundational for understanding the composition of a compound, the molecular formula gives more specific information about its structure.

To determine these formulas, as we did for compound A, you would start with the percent composition by mass of each element. These percentages are converted to moles, which then can be used to find the simplest whole-number ratio and, thus, the empirical formula.

Deducing Formulas from Mass Percentages

In the exercise, we calculated the mole ratio of carbon to hydrogen in compound A using the mass percentages. This simple ratio led to the empirical formula CH₂. If given the molar mass of the compound, we could then derive the molecular formula. However, if the empirical formula’s molar mass is already close to the known molar mass of the compound, it implies that the empirical and molecular formulas are the same. This understanding is essential in identifying unknown compounds and predicting the quantities of products from known amounts of reactants in a chemical reaction.