Notes, summaries, assignments, exams, and problems for Chemistry

Key Properties of Chemical Substances

Ionic Compounds

• Solid at room temperature
• Form crystal lattices, not individual molecules
• Soluble in water
• Conduct electricity when molten or dissolved
• High hardness and brittle
• High melting and boiling temperatures

Molecular Substances

• Composed of molecules
• Weak intermolecular forces
• Often gaseous (e.g., O₂, N₂, NH₃) or liquid (e.g., H₂O)
• Soft solids
• Low melting and boiling temperatures
• Poor electrical conductors
• Not very soluble in water

Covalent Crystals

• Solid
• Form crystals with atoms joined by covalent bonds in three dimensions
• Insoluble in all solvents
• Generally do not conduct electricity (except graphite)
• Very hard and brittle
• High melting and boiling temperatures (1200 to 3600 °C)

Metals

• Solid at room temperature (except

Understanding Uranium and Nuclear Fuel

Natural uranium is composed of three isotopes: Uranium-238 (U-238), Uranium-235 (U-235), and Uranium-234 (U-234). While U-238 is fertile and can be converted to fissile material, U-235 is the primary fissionable isotope used for power generation. Natural uranium ore cannot be used directly as nuclear fuel because the concentration of U-235 is too low. Therefore, uranium needs to be enriched to achieve a U-235 concentration of more than 3%. To produce one kilogram of enriched uranium, approximately eight kilograms of natural uranium must be purified and refined.

How Nuclear Power Plants Operate

Nuclear power plants utilize uranium as their primary energy source, harnessing nuclear fission to generate electricity.... Continue reading "Nuclear Energy Fundamentals: Fuel Cycle, Power, and Waste" »

The Greenhouse Effect

The Greenhouse Effect refers to the increase in a planet's temperature caused by solar heat retained by gases in its atmosphere.

Electromagnetic Waves and Spectrum

Electromagnetic wave propagation is the form of electromagnetic radiation traveling through space. The Electromagnetic Spectrum is a set of waves ranging from the longest (radio waves) to the shortest (gamma rays).

Human Actions Causing Air Pollution

Significant human activities contribute to air pollution:

• Burning fossil fuels like oil or coal
• High traffic densities in cities
• Agricultural activities such as rice fields or swamps
• Industrial processes
• High-tension power lines, telephone antennas, and artificial lighting

The Miller Experiment

In the 1950s, an experiment was... Continue reading "Fundamental Scientific Concepts: From Cosmos to Earth" »

The Electrical Nature of Matter

Thales of Miletus observed that rubbing amber with a cloth caused both to attract other particles. Benjamin Franklin later suggested that all bodies possess electricity, which can be transferred between them. The three primary methods of electrification are friction, contact, and induction.

The amount of electric charge (Q) is a physical quantity, measured in Coulombs (C). There are two types of electric charge: negative (as found in amber or plastic) and positive (as found in glass). Neutral bodies possess an equal number of positive and negative charges.

Coulomb's Law

Coulomb's Law quantitatively calculates the electric force using the following formula:

F = k * Q1 * Q2 / r²

Where:

• F: Force
• k: Constant of the medium
• Q1

Tuberculosis: Diagnosis and Microscopic Examination

Tuberculosis (TB) is a highly contagious infection, primarily pulmonary, caused by members of the Mycobacterium tuberculosis complex.

Causative Agents of Tuberculosis

• Mycobacterium tuberculosis
• M. bovis
• M. avium
• Atypical Mycobacteria

M. avium and atypical mycobacteria are significant opportunistic pathogens, particularly in immunocompromised individuals, transplant recipients, or those undergoing major surgery.

Sputum Sample Collection for Smear Test

1. Obtain at least two sputum samples.
2. Samples can be collected on successive days and stored in a cool, dark place.
3. The sample must be bronchial sputum, not saliva or nasal mucus.
4. Upon waking and before eating, perform a mouthwash with water only.
5. Expectorate

Mol is the quantity of a substance defined by Avogadro's constant, which indicates the number of particles, such as atoms, molecules, and ions. One mole equals 6022 particles.
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Reaction Types:
a) The reorganization of atoms:
1) Synthesis Reaction: Two substances combine to create a new form.
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2) Decomposition Reactions: A substance is broken down into simpler components.
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3) Single Displacement Reactions: An element replaces another in a compound.
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4) Double Displacement Reactions: The positions of two substances are exchanged.
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a) The Reaction Mechanism:
1) Acid-Base Reactions:
* Acids:... Continue reading "Understanding Chemical Reactions and Stoichiometry" »

Chemical Kinetics

Reaction Rate: The change in the concentration of reactants or products per unit time.

For a reaction aA + bB → cC + dD, the rate (v) can be expressed as:

v = -1/a * Δ[A]/Δt = -1/b * Δ[B]/Δt = 1/c * Δ[C]/Δt = 1/d * Δ[D]/Δt

Rate Law: The relationship between the reaction rate and the concentrations of reactants.

v = k [A]^m[B]ⁿ

Where k is the rate constant, and m and n are the reaction orders with respect to A and B, respectively.

Factors Influencing Reaction Rate

• Nature of Reactants: The physical state and chemical properties of reactants affect the rate. Homogeneous reactions (same phase) are often faster than heterogeneous reactions (different phases). In heterogeneous reactions, increasing the surface area increases the

Understanding Hard Water

Older generations coined the phrase "hard water" because its mineral content makes cleaning more difficult. This difficulty is primarily due to dissolved compounds containing calcium and magnesium. Freshwater sources naturally contain varying quantities of these minerals.

As water travels, it dissolves, suspends, or exchanges compounds and trace elements from the materials it contacts. For example, flowing through limestone increases water hardness, while contact with peat can soften it.

Total Water Hardness

Total water hardness measures the combined concentration of calcium and magnesium, the two most common divalent metal ions. However, in some geographic locations, iron, aluminum, and manganese may also be present at... Continue reading "Hard Water Explained: Causes, Types, and Classification" »

Types of Solid Solutions

Metal alloys are solid solutions between two or more elements. Depending on the arrangement of solvent and solute atoms, there are two types:

• Substitution Solid Solutions: Solvent and solute atoms have similar crystalline structures. Solute atoms replace solvent atoms within the crystal lattice.
• Interstitial Solid Solutions: Occur when solute atoms are very small compared to solvent atoms and are placed within the crystal lattice.

Constitution of Fe-C Alloys

Fe-C alloys are composed of constituents whose nature varies with chemical composition and temperature. The most representative constituents are:

• Ferrite: A solid solution of carbon in alpha iron.
• Cementite: The hardest and most brittle constituent of steel.
• Pearlite: A