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

Chlorides

Chlorine, as an element, has a huge tendency to form the chloride ion (Cl^-, a chlorine atom with a negative charge). This ion, in turn, will tend to form salts with other positively charged elements or cations (Na⁺ sodium, K⁺ potassium, Mg²⁺ magnesium, etc.). The chloride ion is one of the main inorganic anions in natural water and wastewater. The chloride content of water is variable and is mainly due to the nature of the terrain traversed. Typically, the chloride ion content of natural waters is less than 50 mg/L. In drinking water, the salt produced by the Cl^- is variable and depends on the water chemistry.

Chlorite and Chlorate

These are salts derived from chloric acid and chlorous acid. These compounds tend to form chlorine gas,... Continue reading "Chloride: Properties, Uses, and Health Effects" »

Chemical Kinetics and Reaction Rates

Factors Influencing Reaction Velocity

• Rate Equation: V = k · [A]^a · [B]^b
• Temperature: The Arrhenius Law: k = k₀ · e^{-E_a / (R · T)}
• Concentration and Pressure: P · V = n · R · T
  P = (n · R · T) / V → n / V = concentration
  P = [X] · R · T
• Standard State and Physical State:
  • Solid: Few collisions result in slow reactions. The level of division is key; more particles mean a greater impact surface.
  • Liquid: Average collision frequency results in average reaction speeds.
  • Gas: Many collisions result in faster reactions.
• Catalysts: Positive catalysts increase speed. Negative catalysts (inhibitors) slow it down. Catalysts do not change thermochemical quantities (ΔH, ΔG, ΔS...), the quantity of product, or

Ranking Elements

The first classification of chemical elements was based on their chemical and physical properties, dividing them into two large groups: metals and non-metals.

• The first classification was done by J.W. Döbereiner. He observed a link between the atomic mass and properties of elements such as barium, calcium, and strontium. He arranged 40 elements in a line, one after another, by their mass.
• John Newlands arranged the elements by atomic mass, from the lowest to the highest, in columns. This is now called the Law of Octaves.
• D.I. Mendeleev arranged the elements by atomic mass. As a result of this work, the periodic law of elements was discovered in 1869.

Forces Between Molecules

These are listed from weakest to strongest:

1. Dispersion

Minerals and Alloy Fundamentals

Minerals: A usable part is formed by the metal and rich-looking material, named the ore, and another not usable part because it is very poor in metal, called the gangue (bargain).

Alloys: A product obtained from the union of two or more chemical elements which presents the characteristics of a metal. An alloy modifies its crystalline structure, increasing its hardness and mechanical resistance but lowering its conductivity.

Solidification of Alloys

• Area liquid phase: Liquidus line for liquid (it will always be liquid).
• Area solid + liquid phase: Contains a mass of solid and another of liquid.
• Solid-phase area: Below the solidus line (always a solid phase).

Classification of Metal Products

Shop-metal products:

• Ferrous

Atomic Structure: Models and Definitions

The Plum Pudding Model

The Plum Pudding Model considers the atom as a ball of positive charge with electrons (negative charge) embedded.

The Rutherford Model

Rutherford's Bombardment Experiment

Rutherford tested the Rutherford Model by bombarding metal foil atoms with alpha particles (projectiles harder than atoms).

Experimental Results

• Result 1: The majority of alpha particles passed through the foil undeflected.
• Result 2: Some of these particles suffered deviation.
• Result 3: Very few rebounded and turned back.

Interpretation and Consequences

The interpretation was that particles that crossed the foil showed that atoms are not solid, but contain much empty space.

The Consequences of the Rutherford Atomic Model... Continue reading "Atomic Structure Fundamentals: Models, Particles, and Radioactivity" »

Reactions in Aqueous Solutions

Acid and Base Definition According to Bronsted-Lowry

Acid: A substance capable of donating protons.

Base: A substance capable of accepting protons.

For a substance to act as an acid, it must be in the presence of another substance that acts as a base and accepts the proton transferred by the acid. In aqueous solutions, water plays the role of both acid and base.

• When an acid donates protons, it becomes a species capable of accepting protons, called the conjugate base.
• When a base accepts protons, it is transformed into a species capable of donating protons, i.e., an acid, called the conjugate acid.

Equilibrium of Water Dissociation and the Concept of Kw

Water behaves as both an acid and a base according to the reaction:... Continue reading "Chemical Reactions in Aqueous Solutions and Stoichiometry" »

Fundamental Atomic Definitions

• Atom: The smallest unit of a chemical element that retains its identity and properties, which cannot be split by chemical processes.
• Element: A substance composed of identical atoms.
• Compound: A substance made up of different atoms combined in a specific numerical relationship.

The Bohr Model of the Atom

Taking the Rutherford model as a starting point, Niels Bohr sought to incorporate the phenomena of gas absorption and emission, alongside the new theory of energy quantization developed by Max Planck. The atom is described as a miniature solar system with a nucleus at the center and electrons moving in well-defined orbits.

• Each orbit has an associated energy level; the further the orbit is from the nucleus, the higher

Atomic Structure Concepts

Balmer Series

The striped visible emission spectrum of H corresponds to the transitions of excited electrons returning to level n = 2.

Lyman Series

If electrons transition to level n = 1, the energy differences are greater, resulting in higher frequencies. The lines of this spectrum appear in the ultraviolet region.

Quantum Model and Orbitals

Quantum Model

An electron with a given energy sublevel occupies a defined region of space called an orbital.

Orbital Definition

An orbital is a region of space where there is a high probability of finding the electron.

Form of an Orbital

The form of an orbital depends on the type of sublevel (q) it belongs to. S orbitals are spherical; P orbitals are dumbbell-shaped (often described as '... Continue reading "Atomic Structure and Chemical Laws Explained" »

Conventional Thermal Power Plant Operation

Electric power is generated from the heat produced by the combustion of coal or natural gas fuel.

Core Components of the Thermoelectric Cycle

There are many types of boilers. The most commonly used are radiation boilers, so named because the heat energy is primarily transmitted by radiation.

Boiler Structure and Function

Boilers have a burner appropriate for the type of fuel used and a combustion chamber surrounded by innumerable tubes through which water circulates to vaporize.

Reheaters

Reheaters are parts of the boiler designed to eliminate water droplets accompanying the steam to convert it into dry steam.

Economizers and Preheaters

Economizers and preheaters harness the residual heat of the emitted combustion... Continue reading "Thermal Power Generation Plant Components and Cycle" »

Elements and Compounds

Elements are substances consisting of a single type of atom. Compounds are substances obtained by the grouping of atoms of different elements.

A Little History

Chemical Elements for Life: Bioelements

Bioelements are the chemical elements of living beings. The most abundant species are: C, H, O, N, Ca, P, Mg, S, Na, K, and Cl, and they make up more than 99% of these living things.

Trace Elements

Trace elements are present in lower proportions (approximately 0.1%) and are indispensable for all living things, such as Fe, Zn, Mn, F, I, Cu, and Co.

The RDA (Recommended Dietary Allowance) is the amount of nutrient that a healthy person should eat each day on average, as part of the diet, to maintain good health.

Isolated Atoms

The elements... Continue reading "Fundamental Chemical Substances and Structures" »