Chemical Quantities and Reactions – General Chemistry Chapter 7 Study Notes

Chemical Quantities and Reactions

Introduction

This chapter introduces the fundamental concepts of chemical quantities, including the mole, Avogadro's number, molar mass, and their applications in chemical reactions. Understanding these concepts is essential for quantifying substances and interpreting chemical equations in general chemistry.

The Mole and Avogadro's Number

Definition of the Mole

The mole is a standard scientific unit for measuring large quantities of very small entities such as atoms, molecules, or ions. It allows chemists to count particles by weighing them.

• Avogadro's number is the number of particles in one mole of a substance.

• Avogadro's number: $6.02 \times 10^{23}$ particles/mole

• Named after Amedeo Avogadro, an Italian physicist.

Equality and Conversion Factors

Avogadro's number can be used to convert between moles and number of particles.

• Equality: $1 \text{ mole} = 6.02 \times 10^{23} \text{ particles}$

• Conversion factors:

  • $\frac{1 \text{ mole}}{6.02 \times 10^{23} \text{ particles}}$

  • $\frac{6.02 \times 10^{23} \text{ particles}}{1 \text{ mole}}$

Example: Converting Moles to Molecules

To find the number of molecules in a given number of moles, multiply the moles by Avogadro's number.

• How many CO2 molecules are in 1 mole of CO2? $1 \text{ mole} \times 6.02 \times 10^{23} \text{ molecules/mole} = 6.02 \times 10^{23} \text{ molecules}$

Counting Atoms and Moles

Sample Calculations

• Number of atoms in 2.0 moles of Al: $2.0 \text{ moles} \times 6.02 \times 10^{23} \text{ atoms/mole} = 1.2 \times 10^{24} \text{ atoms}$

• Number of moles in $1.8 \times 10^{24}$ atoms of S: $\frac{1.8 \times 10^{24} \text{ atoms}}{6.02 \times 10^{23} \text{ atoms/mole}} = 3.0 \text{ moles}$

Moles of Elements in a Chemical Formula

Subscripts and Mole Relationships

Subscripts in a chemical formula indicate the number of atoms of each element in one molecule and the number of moles of each element in one mole of the compound.

• For aspirin ($\mathrm{C}_9\mathrm{H}_8\mathrm{O}_4$):

  • 1 molecule: 9 atoms of C, 8 atoms of H, 4 atoms of O

  • 1 mole: 9 moles of C, 8 moles of H, 4 moles of O

Example Calculation

• How many atoms of O are in 0.150 mole of aspirin? $0.150 \text{ mole aspirin} \times \frac{4 \text{ moles O}}{1 \text{ mole aspirin}} \times 6.02 \times 10^{23} \text{ atoms O/mole O}$

Molar Mass

Definition and Calculation

Molar mass is the mass of one mole of an element or compound, expressed in grams. For elements, it is numerically equal to the atomic mass in grams.

• Example: 1 mole of C atoms = 12.01 g of C atoms

• Equality: $1 \text{ mole C} = 12.01 \text{ g C}$

Application

• Used to convert between mass and moles of a substance.

• Essential for stoichiometric calculations in chemical reactions.

Summary Table: Key Conversion Factors

Quantity	Conversion Factor
Moles to Particles	$1 \text{ mole} = 6.02 \times 10^{23} \text{ particles}$
Moles to Mass	$1 \text{ mole} = \text{molar mass (g)}$
Formula Subscripts	Subscript = moles of element per mole of compound

Additional info:

• These notes cover the first part of Chapter 7, focusing on chemical quantities, the mole concept, Avogadro's number, and molar mass. Later sections (not shown in the images) typically include chemical equations, reaction types, stoichiometry, and energy changes in reactions.