BackChemical Quantities and Reactions: Study Notes for GOB Chemistry
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Chapter 7: Chemical Quantities and Reactions
Avogadro's Number
Avogadro's number is a fundamental constant in chemistry used to count very small particles such as atoms, molecules, and ions. It defines the number of particles in one mole of a substance.
Definition: Avogadro's number is particles per mole.
Equality:
Conversion Factors:
Application: Used to convert between moles and number of particles (atoms, molecules, ions).
Historical Note: Named after Amedeo Avogadro (1776–1856), Italian physicist.
Converting Moles to Molecules
Avogadro's number allows chemists to convert between the amount of substance in moles and the actual number of molecules or atoms present.
Example: How many molecules are in 0.50 mole of CO2?
Moles of Elements in a Formula
The subscripts in a chemical formula indicate the number of atoms of each element in one molecule, and thus the number of moles of each element in one mole of the compound.
Example: Aspirin, C9H8O4
1 molecule: 9 atoms C, 8 atoms H, 4 atoms O
1 mole: 9 moles C, 8 moles H, 4 moles O
Calculating Atoms in a Compound
To find the number of atoms of a specific element in a given amount of compound, use the mole ratio from the formula and Avogadro's number.
Example: How many atoms of O are in 0.150 mole of C9H8O4?
Molar Mass
The molar mass is the mass of one mole of an element or compound, expressed in grams per mole (g/mol). It is numerically equal to the atomic or molecular mass in atomic mass units (amu), but expressed in grams.
Definition: Molar mass is the mass of 1 mole of a substance.
Example: Carbon (C):
Calculating Molar Mass of Compounds
To calculate the molar mass of a compound, sum the atomic masses of all atoms in the formula, multiplied by their subscripts.
Example: Lithium carbonate, Li2CO3:
Summary Table: Moles and Particles
This table summarizes the relationships between moles, mass, and number of particles.
Quantity | Conversion Factor |
|---|---|
Moles to Particles | |
Moles to Mass | |
Particles to Moles | |
Mass to Moles |
Key Terms
Mole: The SI unit for amount of substance, equal to particles.
Avogadro's Number: , the number of particles in one mole.
Molar Mass: The mass of one mole of a substance, in grams per mole.
Subscript: The small number in a chemical formula indicating the number of atoms of each element.
Practice Problems
Convert moles to number of particles using Avogadro's number.
Calculate the molar mass of a compound from its formula.
Determine the number of atoms of a specific element in a given amount of compound.
Additional info: These notes cover the foundational concepts of chemical quantities, including the mole concept, Avogadro's number, and molar mass, which are essential for understanding chemical reactions and stoichiometry in GOB Chemistry.
