Ch.3 - Chemical Reactions and Reaction Stoichiometry

Brown - Chemistry: The Central Science 15th Edition

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Brown 15th Edition

Ch.3 - Chemical Reactions and Reaction Stoichiometry

Problem 31

Chapter 3, Problem 31

Without doing any detailed calculations (but using a periodic table to give atomic weights), rank the following samples in order of increasing numbers of atoms: 0.50 mol H₂O, 23 g Na, 6.0⨉10²³N₂molecules.

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Identify the number of atoms in one molecule of each substance: H2O has 3 atoms (2 H and 1 O), Na has 1 atom, and N2 has 2 atoms.

Calculate the number of molecules in 0.50 mol of H2O using Avogadro's number (6.022⨉10^23 molecules/mol).

Determine the number of atoms in 0.50 mol of H2O by multiplying the number of molecules by the number of atoms per molecule.

Convert 23 g of Na to moles using the atomic weight of Na (approximately 23 g/mol) and then calculate the number of atoms using Avogadro's number.

For 6.0⨉10^23 N2 molecules, calculate the total number of atoms by multiplying the number of molecules by the number of atoms per molecule (2 atoms per N2 molecule).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Moles and Avogadro's Number

A mole is a unit in chemistry that represents 6.022 x 10²³ entities, such as atoms or molecules. This concept is crucial for converting between the number of moles and the number of individual particles. Understanding moles allows us to compare different substances based on the number of atoms or molecules they contain.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is essential for converting between mass and moles, enabling the calculation of the number of atoms in a given mass of a substance. For example, knowing the molar mass of water (H₂O) helps determine how many moles are present in a specific mass.

Stoichiometry

Stoichiometry is the area of chemistry that deals with the relationships between the quantities of reactants and products in chemical reactions. It allows for the calculation of the number of atoms or molecules in a sample based on the balanced chemical equations and the amounts of substances involved. This concept is vital for ranking the samples in the question based on their atomic content.

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