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

Defrosting is essential in refrigeration systems to remove ice accumulation on evaporators, which reduces efficiency and cooling capacity.

Natural Defrosting

This method is typically used in refrigerated spaces operating above +2°C. It involves stopping the refrigeration system (compressor and fans) for a period, allowing the warmer ambient air within the refrigerated space to melt the ice accumulated on the evaporator.

In low-temperature facilities for freezing and storage of frozen products, based on forced-air evaporators, it becomes necessary to create additional heat for defrosting to melt the ice.

Water Spray Defrosting

This method involves spraying water under pressure onto the ice accumulated on the evaporator. The water melts the ice and... Continue reading "Refrigeration Defrost Methods" »

Hemoglobin Iron Environment and Geometry

The iron ion (Fe) in Hemoglobin (Hb) is in a square planar environment, bonded to four nitrogen (N) atoms of the porphyrin ring. The fifth coordination position is bound to a nitrogen atom from a histidine residue (perpendicular to the plane), and the sixth position binds O₂ in oxyhemoglobin. When oxygenated, the coordination geometry around the iron is essentially octahedral. In contrast, deoxygenated Hb has a five-coordinate, square pyramidal geometry, as the sixth position is vacant.

Role of Magnesium and Calcium Competition

Magnesium (Mg) is extremely important. It plays a role related to the Na⁺/K⁺ pump; the interior of the cell requires large amounts of K⁺ and low amounts of Na⁺. Mg facilitates the... Continue reading "Iron and Copper Roles in Biological Oxygen Transport" »

Atoms, Molecules, and Ions

Atoms: Electrically balanced particles consisting of one positively charged center called the nucleus, surrounded by a cloud of negatively charged particles called electrons, which exactly balance the nuclear charge.

Molecules: Electrically balanced particles with more than one positive center (nuclei). Molecules are sets of bonded atoms that act as a unit.

Ions: Atoms (or groups of atoms) with unbalanced charges.

The number of protons determines the number of electrons necessary to balance the atom's charge. Neutrons are the cementing material in the nucleus. The force between protons and neutrons is called the strong nuclear interaction. Number of protons = ATOMIC NUMBER of the atom (Z)

The atomic number is also given... Continue reading "Understanding Atoms, Molecules, and Ions: Structure and Properties" »

1. True or False Statements

a) True

b) True

c) True / FALSE, if the hypothesis has not been demonstrated.

2. Measurement Units and Properties

a) Size: m³ is a unit of volume and can be used in moderation.

b) Scalability: It does not scale; it is not a unit of restraint.

c) Magnitude Measurement: Magnitude can be measured in K (Kelvin).

3. Units of Measurement

• Length - Meter - m
• Mass - Kilogram - kg
• Time - Second - s
• Temperature - Kelvin - K
• Intensity of Current - Ampere - A

4. Unit Conversions

a) 2.5 mm x (1 m / 1,000 mm) = 0.0025 m = 2.5 x 10^-3 m

b) 0.53 mg x (1 g / 1,000 mg) x (1 kg / 1,000 g) = 0.00000053 kg = 5.3 x 10^-7 kg

c) 3 h x (3,600 s / 1 h) = 10,800 s = 1.08 x 10⁴ s

5. Calculations with Significant Figures

a) 8.34 x 3.1456 = 26.234304 = 26.2

b) 4.00... Continue reading "Understanding Physical Quantities and States of Matter" »

Introduction to Chemistry

Chemistry is the science of matter and its properties, including its composition, structure, physical properties, and reactivity. It involves observation, knowledge, and reasoning to deduce general principles and laws.

Types of Chemistry

1. Experimental:

• Natural: Physics, Chemistry, Biology
• Human: Geography, Politics, History

Formal: Mathematics and Logic

The scientific method involves observation, gathering information, forming a hypothesis, conducting experiments (with independent, dependent, and control variables), analyzing results, and developing a theory or law.

Conversions:

• 1 lb = 0.454 kg
• 1 in = 2.54 cm
• 1 in² = 6.45 cm²

Chemical Compounds

• Hydroacids (H + NM)
• Binary Salts (M + NM)
• Hydrides (M + H)
• Non-metal Oxides (NM + O)
• Metal

... Continue reading "Understanding Chemistry: Formulas, Reactions, and Concepts" »

Planck's Theory

The energy emitted by radiation is directly proportional to the frequency of radiation.

Bohr Model

Postulates:

1. Electrons revolve around the nucleus in circular orbits without emitting energy.
2. Electrons are only allowed in orbits where their angular momentum is a multiple of h/2π.
3. When an electron moves between orbits, the energy difference is emitted as radiation.

Bohr determined the radius, energy, and location of electrons within these orbits.

Sommerfeld's Modifications

Sommerfeld modified the Bohr model to include elliptical orbits. He introduced a second quantum number, which depends on the first and describes the orbit's shape.

l = 0 ... (n-1)

Zeeman Effect: When an atomic spectrum is subjected to a magnetic field, spectral lines... Continue reading "Atomic Structure and Quantum Mechanics" »

Understanding Atoms: Key Concepts

Atom: The smallest unit of a chemical element that retains its identity and properties, and cannot be split by chemical processes.

Mass Number: Represents the sum of protons and neutrons present in the atomic nucleus. Also known as the nucleon number.

Atomic Number: The positive integer that equals the total number of protons in an atom's nucleus.

Ion: A particle formed when a neutral atom or group of atoms gains or loses one or more electrons.

Cation: An ion (either atom or molecule) with a positive electric charge.

Anion: An ion (either atom or molecule) with a negative electric charge.

Isotope: Used to indicate that all isotopes of the same element are found in the same place in the periodic table.

Atomic Mass:... Continue reading "Understanding Atoms: Mass, Number, Ions, and Isotopes" »

States of Matter and Their Changes

State changes are processes experienced by the body according to the environmental conditions of pressure and temperature.

• Solid-Liquid (Fusion)
• Liquid-Gas (Vaporization)
• Gas-Solid (Deposition)
• Liquid-Solid (Solidification)
• Solid-Gas (Sublimation)
• Gas-Liquid (Condensation)

When heating a body, the energy of the particles increases. There comes a moment when this energy is sufficient to overcome the forces of cohesion, and then fusion occurs when we consider that part of a solid body. The same applies to all states of aggregation. The form of fusion of a body depends on its nature. We will distinguish between crystalline and amorphous bodies.

• In a crystalline body, such as ice, melting is produced at a constant temperature

... Continue reading "Understanding Matter: States, Changes, and Mixtures" »

Atomic Theory: From Democritus to Quantum Models

Democritus' Atomic Theory

Democritus, in ancient Greece, founded the atomist school. This school, taking a pluralistic approach, proposed that atoms were the fundamental particles. The core principles of atomism are:

1. Atoms move in a vacuum.
2. The shape and size of atoms determine the substance.

Aristotle, conversely, believed that matter was a single, continuous entity.

Dalton's Atomic Theory

John Dalton proposed his atomic theory in the early 19th century. Its key postulates are:

1. Elements are composed of indivisible and indestructible particles called atoms.
2. Atoms of the same element have the same mass and properties.
3. Atoms of different elements have different masses and properties.
4. Chemical compounds are

... Continue reading "Democritus to Quantum Models: Atomic Theory Explained" »

Understanding Material Systems and the Atmosphere

Background: A material system is a set of interrelated elements considered as a unit for study.

Homogeneous and Heterogeneous Material Systems

Material systems can be homogeneous or heterogeneous.

In a homogeneous system, different substances are not readily apparent.

A mixture is a material system (either homogeneous or heterogeneous) from which different substances can be separated by physical processes.

Solutions and Their Components

A solution is a homogeneous mixture formed by two or more substances in variable amounts, which can be separated by physical means.

In a solution, the substance present in the greater proportion is called the solvent; the others are called solutes.

Separation Techniques

... Continue reading "Understanding Material Systems, Atmosphere, and Air Composition" »