Fundamental Constants and Units

Physical Constants

Physical constants are essential values used in chemical calculations and problem solving. They provide the basis for quantitative work in chemistry.

• Avogadro's number (Na): mol-1 — the number of particles in one mole of substance.

• Electron charge (e): C — the charge carried by a single electron.

• Electron mass: g — mass of an electron.

• Faraday constant (F): C/mol e- — charge per mole of electrons.

• Gas constant (R): L·atm/(mol·K) or J/(mol·K) — used in gas law calculations.

• Planck's constant (h): J·s — relates energy and frequency in quantum mechanics.

• Proton mass: g — mass of a proton.

• Neutron mass: g — mass of a neutron.

• Speed of light (c): m/s — speed at which light travels in a vacuum.

Useful Conversion Factors and Relationships

Conversions between units are frequently required in chemistry. The following relationships are commonly used:

Pressure Units

Pressure is a key concept in gas laws and solution chemistry. Common units and their relationships:

Equations

Common equations for temperature conversion, density, and molarity:

• Temperature conversions:

• Density:

• Molarity:

Atoms, Elements, and Atomic Theory

Atomic Structure and Subatomic Particles

Atoms are composed of protons, neutrons, and electrons. Their arrangement determines the properties of elements.

• Protons: Positively charged particles found in the nucleus.

• Neutrons: Neutral particles found in the nucleus.

• Electrons: Negatively charged particles found outside the nucleus.

• Atomic number (Z): Number of protons in the nucleus.

• Mass number (A): Sum of protons and neutrons.

Example: Carbon-12 has 6 protons and 6 neutrons.

Dalton's Atomic Theory and Modifications

Dalton's atomic theory laid the foundation for modern chemistry, but has been modified over time:

• Atoms of a given element are identical (now known to be isotopes).

• All matter is made up of very small particles called atoms.

• Compounds are formed from atoms.

• Chemical reactions involve rearrangement of atoms.

Molecules, Compounds, and Chemical Formulas

Chemical Formulas and Nomenclature

Chemical formulas represent the composition of compounds. Nomenclature rules help name compounds systematically.

• Empirical formula: Simplest whole-number ratio of atoms in a compound.

• Molecular formula: Actual number of atoms of each element in a molecule.

• Example: Glucose: Empirical formula CH2O, Molecular formula C6H12O6.

Writing Chemical Formulas

Formulas for compounds are written using element symbols and subscripts to indicate the number of atoms.

• Phosphorous Trioxide: P2O3

• Gold (III) Bromide: AuBr3

• Lithium Permanganate: LiMnO4

• Aluminium Selenide: Al2Se3

• Ammonium Fluoride: NH4F

• Dichlorine Heptoxide: Cl2O7

Chemical Reactions and Stoichiometry

Types of Chemical Reactions

Chemical reactions involve the transformation of substances. Key types include:

• Redox reactions: Transfer of electrons between species.

• Acid-base reactions: Transfer of protons (H+).

• Precipitation reactions: Formation of an insoluble product.

Balancing Chemical Equations

Balancing equations ensures the conservation of mass and charge. Coefficients are used to equalize the number of atoms on both sides.

• Example:

• Balanced:

Stoichiometry and Molarity

Stoichiometry involves quantitative relationships in chemical reactions. Molarity is a measure of concentration:

• Molarity (M):

• Example: To dilute 0.450 M K2CO3 to 0.315 M, use .

Lab Techniques and Problem Solving

Empirical and Percent Composition Calculations

Determining the empirical formula and percent composition is essential for analyzing compounds.

• Percent composition:

• Empirical formula: Find the simplest ratio of moles of each element.

Limiting Reactant and Yield Calculations

Identifying the limiting reactant and calculating theoretical and percent yield are key steps in reaction analysis.

• Limiting reactant: The reactant that is completely consumed first, limiting the amount of product formed.

• Theoretical yield: Maximum amount of product possible from given reactants.

• Percent yield:

Example Problem: Ostwald Process

The Ostwald process for producing nitric acid involves:

• Given masses of reactants, determine limiting reactant, theoretical yield, and percent yield.

Additional info:

• Some questions and problems reference solubility rules, oxidation numbers, and organization of subatomic particles, which are foundational topics in general chemistry.

• Tables have been recreated and expanded for clarity and completeness.