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

Item 7: Energy from Atomic Nuclei

Chemical vs Nuclear Reactions

The energy that comes from atomic nuclei differs from chemical energy. In chemical reactions, changes occur in the distribution of electrons orbiting the nuclei, while nuclear reactions involve changes to the nuclei themselves. Matter cannot be created or destroyed; it is only transformed — in nuclear reactions this transformation releases energy.

Controlling Nuclear Reactions

A common system used to control nuclear chain reactions is the use of a moderator, which slows neutrons and helps regulate the fission process.

Technical Achievements of Nuclear Energy

Reactor Classification

Nuclear reactors are classified according to several criteria:

• By neutron speed

  Thermal reactors and fast

Chemicals

Evaporation

Evaporation is a physical process involving a state change from liquid to gas, in which substances can be separated based on their boiling points.

For the transition of a liquid to a gaseous state from liquid surfaces or from the ground, see: Evaporation (hydrology).

Redox

Oxidation-reduction reactions (also known as redox reactions) are electron transfer reactions. This transfer occurs between a set of chemical elements: an oxidant and a reductant (a reduced form and an oxidized form, respectively).

For a redox reaction to occur, the system must contain an element that yields electrons and another that accepts them:

• The oxidizing agent is a chemical element that tends to capture these electrons, resulting in a lower oxidation

Fundamentals of Solid-Liquid Extraction

Key Applications in Various Industries

• Extraction of sugar from sugar beets
• Coffee decaffeination
• Extraction of essential oils from herbs and botanicals
• Recovery of oils from seeds and other materials
• Obtaining pectin (for jelly) from fruit fractions

Commonly Used Solvents

• Water
• Hexane
• Heptane
• Ether
• Chloroform
• Benzene
• Ethanol

Industrial Extractor Equipment Designs

Static Bed Extractors

These extractors operate with a stationary solid bed through which the solvent passes.

Simple Contact Extractors

These operate discontinuously and are simple in design. They consist of a double-bottom tank where the solid material is placed. A liquid solvent is sprayed over the solid and percolates through it by gravity. The solvent, now... Continue reading "Industrial Extractor Technologies: Methods & Applications" »

Seven Primary Dimensions

There are 7 primary dimensions:

• Length (meter, m)
• Mass (kilogram, kg)
• Time (second, s)
• Temperature (kelvin, K)
• Electrical Current (ampere, A)
• Light Intensity (candela, cd)
• Amount of Substance (mole, mol)

Note: 1 liter (l) equals 1 cubic decimeter (dm³).

The Scientific Method

A) Observation

Please note: Asking questions begins by observing phenomena perceived through our consciousness. Observation implies curiosity.

B) Formulation of Hypotheses

Hypotheses are possible answers to the questions raised during observation.

C) Experimentation

Experimentation checks whether the assumptions made are true or false. In this stage, perform the following:

1. Design and assembly of experiments.
2. Data collection.
3. Measurement of quantities.

D) Analysis of

Previous Concepts

Stress: The applied force per unit area.

Elongation: Deformation of a material under the action of a force.

Reduction in Area: The decrease in cross-sectional area.

General Properties

• Impenetrability: The volume occupied by a body cannot be occupied by another simultaneously.
• Severability: Divisible parts can be increasingly smaller.
• Porosity: Having pores.
• Compressibility: The ability of bodies to decrease their volume by applying pressure.
• Affinity: The force that unites similar materials.
• Adhesion: Attraction established between bodies whose surfaces are in contact.
• Solubility: The ability to dissolve and disperse within a liquid.
• Specific Gravity: The ratio of a body's weight to the weight of an equal volume of a reference substance.

Atoms, Bonding, and Molecular Crystals

Ancient history knew elements such as gold, silver, etc. Over time, more elements were discovered; currently, over a hundred are known. A basic classification of elements, based on their appearance and physical properties, allows us to divide them into two main groups: metals and non-metals.

Metals and Non-Metals

To distinguish these groups, we examine their differing characteristic features.

1. Metallic Elements

• They have a characteristic luster.
• They are opaque and good conductors of heat and electricity.
• They are solid at ambient temperature and usually tend to have high melting points.

2. Non-Metallic Elements

• They do not have metallic luster.
• They are poor conductors of heat and electricity.
• At ambient temperature,

Fundamental Atomic Concepts

Atomic Number and Mass Number

Two fundamental properties of an atom are its atomic number and mass number.

• The Atomic Number (Z): This is the number of protons in the nucleus of an atom. For example, a neutral Sodium atom (Na) with atomic number 11 has 11 protons and 11 electrons.
• The Mass Number (A): This is the total number of protons and neutrons in the nucleus of an atom. For example, Sodium-23 (²³Na) has a mass number of 23.

The number of neutrons can be calculated by subtracting the atomic number from the mass number (A - Z).

The Atom, Molecule, and Orbitals

The Atom

In physics and chemistry, an atom is the smallest unit of a chemical element that retains its identity and properties. It cannot be divided further by... Continue reading "Atomic Structure and Electron Configuration Principles" »

Atomic Model Evolution

Democritus's Atomic Theory

Democritus proposed that matter could not be divided into smaller pieces forever. He believed that there were tiny, eternal, invisible, and indivisible particles called atoms (meaning indivisible in Greek) that constituted all matter.

Dalton's Atomic Theory (1808)

• Matter is made of indivisible and indestructible particles called atoms.
• All atoms of an element are identical.
• Atoms of different elements combine in fixed proportions to form compounds.

Thomson's Atomic Model (1897)

J.J. Thomson experimentally verified the existence of the electron. He discovered that the electron's mass was much lower than that of atoms, suggesting that atoms possessed a negative charge and were divisible. His model described... Continue reading "Atomic Model Evolution and Chemical Bonding" »

Other Contributions to the New Worldview

Tycho Brahe: His astronomical observations were accurate enough in the long run to support heliocentric theses. His findings were inconsistent with the belief in Aristotelian spheres and the immutability of the cosmos. Brahe discovered a new star in the constellation Cassiopeia, destroying the notion that the supralunar world is free from generation and corruption; he also mapped the orbits of comets.

Johannes Kepler and Elliptical Orbits

Johannes Kepler, a disciple of Brahe, was an enthusiastic supporter of heliocentrism. He formulated a series of laws that moved away from the Aristotelian inheritance maintained by Copernicanism, specifically the circularity of orbits and the uniformity of their velocity.... Continue reading "Scientific Revolutions: Heliocentrism and Quantum Physics" »

Understanding Human Growth Curves and Body Types

4.1. The Emerging Growth Curve

Each variable of interest (weight, height, etc.) can be related to different ages, defining what is called the emerging growth curve. This curve is intended to gain insight into the process of the acquisition of some variables over the years.

4.2. The Velocity Curve: Measuring Physical Growth Rate

The velocity curve (or physical growth curve) shows the amount gained (rate) each year (e.g., in cm, g, or kg). In a typical curve of growth rate, specific moments are expressed:

• Slowdown
• Stability
• Acceleration
• Culmination point of growth (peak velocity)
• Final growth stage

4.3. Body Proportions and Differential Growth Rates

In the study of human growth, the body and its parts do... Continue reading "Human Growth and Development: Curves, Rates, and Somatotype Classification" »