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

Understanding Energy Fuels and Combustion

Energy fuels are substances capable of releasing energy in the form of heat through combustion or, in the case of nuclear fuels, through nuclear reactions. Most fuels used in engineering are hydrocarbons composed of carbon and hydrogen, although they may also contain oxygen, nitrogen, or sulfur—elements that influence their thermal behavior and the emissions they produce.

Solid Fuels and Coal Composition

Among solid fuels, coal stands out, composed of organic matter, mineral compounds, and different types of moisture. The presence of moisture and ash reduces its quality, as they do not provide useful energy and require additional heat to evaporate. To analyze coal, two fundamental parameters are used:... Continue reading "Energy Fuels: Properties, Types, and Efficiency" »

Fundamentals of Separation Processes

Separation processes are crucial in chemical engineering for purifying substances and isolating components. This section defines key concepts in adsorption, ion exchange, crystallization, and membrane technology.

Understanding Adsorption Principles

1. What is Adsorption? Adsorption is the accumulation of substances from a fluid (gas or liquid) onto the surface of a solid or liquid (the adsorbent), forming a thin film.

Defining Physisorption and Chemisorption

2. Defining Physisorption and Chemisorption:

• Physisorption: Involves weak van der Waals forces, is reversible, and typically occurs at low temperatures.
• Chemisorption: Involves chemical bond formation, is usually irreversible, and occurs at higher temperatures.

Collision theory 

- In order for a successful collision to occur, they must collide with the right amount of energy, and in the right orientation

       - Not all collisions are effective, only those that meet the minimum activation energy are effective

- The reaction rate also depends on how frequently reactant molecules collide

        - By colliding more often, reactant particles have more opportunities to undergo effective collisions

INCREASE CONCENTRATION OF REACTANTS: 

- More Particles, More Collisions: Higher concentration means more reactant molecules packed into the same volume.

- Increased Frequency: With more particles, the number of collisions occurring per second goes up significantly.

- More Successful Collisions: A greater... Continue reading "Temperature remains unchanged or decreases slightly as altitude is increased?" »

Physical Adsorption (Physisorption)

• It occurs due to weak van der Waals forces between the adsorbent and adsorbate.
• The enthalpy of adsorption is low, typically between 20–40 kJ/mol.
• It is usually non-specific and can occur on many types of surfaces.
• It is reversible in nature and can be undone by changing pressure or temperature.
• Physisorption is favored at low temperatures.
• It can result in the formation of multiple layers of adsorbed molecules.
• Little to no activation energy is required for physisorption.

Chemical Adsorption (Chemisorption)

• It involves the formation of strong chemical bonds (covalent or ionic) between the adsorbent and adsorbate.
• The enthalpy of adsorption is high, ranging from 40–400 kJ/mol.
• It is highly specific and depends on

Discover how to bake incredibly moist and gooey homemade brownies from scratch, achieving a texture similar to your favorite box mix without any artificial additives. This simple recipe highlights key ingredients and techniques for perfect results every time.

Essential Ingredients for Your Brownies

• Vanilla Extract: A half teaspoon of vanilla extract significantly enhances the rich chocolate flavor.
• Eggs + Water: Michelle's secret for a moist, gooey texture, similar to box mix brownies, without commercial emulsifiers. Since this recipe does not contain baking powder, eggs are crucial for helping the brownies rise in the oven.
• Powdered Sugar: The key to achieving that classic box-mix brownie texture! Powdered sugar contains cornstarch, which naturally

Atomic Structure and Isotopes

Proton number: The number of protons in an atom (and the number of electrons in an uncharged atom).
Nucleon number: The total number of protons and neutrons in an atom.

In the periodic table, moving one element to the right increases the proton number by 1. Moving one element down increases the proton number by 8 in the first three periods (excluding transition elements).

Isotopes and Radioactivity

Isotopes: Atoms of the same element that have different numbers of neutrons (e.g., Carbon-12 and Carbon-14).

• Non-radioactive isotopes: Stable atoms.
• Radioisotopes: Unstable atoms that decay and emit radiation.

Applications of Radioisotopes

• Medical: Cancer treatment (radiotherapy) using Cobalt-60 to kill cancer cells.
• Industrial:

Electroanalytical Fundamentals

• Common electroanalytical methods
• Electrochemical cell fundamentals
• Potential in electrochemical cells
  • No current: Nernst Equation
  • With current: Ohmic Resistance and Polarization

What is Potentiometry?

• Potentiometry involves measuring the electrochemical potential between two electrodes in a solution. This potential difference (voltage) is related to the concentration of ions in the solution according to the Nernst Equation.

General Principles of Potentiometry

• Reference Electrode:

  • Known, fixed potential
    • Silver/Silver Chloride (Ag/AgCl)
    • Calomel

• Indicator Electrode:

  • Sensitive to concentration of analyte
    • Metallic
    • Ion-Selective
• Measure E_cell (negligible current flows through the cell)
• Correct E_ref and E_j (Junction Potential)
• Compute

Bohr's Postulates of Atomic Structure

Bohr's Postulates: Electrons in an atom revolve around the nucleus in certain fixed circular paths called orbits. Each orbit has a fixed amount of energy, so these are also called energy levels. These levels are denoted by 1, 2, 3, 4 or K, L, M, N.

As long as an electron revolves around the nucleus in a fixed orbit, it does not emit or absorb energy; therefore, these are also called stationary orbits. The angular momentum of a revolving electron is quantized and is an integral multiple of h/2π:

mvr = nh/2π

Where:

• m = mass of electron
• v = velocity
• r = radius
• h = Planck's constant

Energy is emitted or absorbed when an electron jumps from one orbit to another. The energy difference between two orbits is ΔE = E₂

Defining Creams and Pastes

Creams

Creams are semi-solid emulsions used externally on the skin. They can be either oil-in-water (O/W) or water-in-oil (W/O) emulsions. They are used for moisturizing, healing, or delivering drugs through the skin.

• Example: Cold Cream (W/O), Vanishing Cream (O/W)

Pastes

Pastes are also semi-solid but contain a high amount of insoluble powders (around 25-50%), making them stiffer and more absorptive. They form a protective layer on the skin and are used where longer contact is needed.

• Example: Zinc Oxide Paste

Understanding Pharmaceutical Aerosols

Aerosols are pressurized dosage forms that release active ingredients as a fine spray, mist, or foam when a valve is opened. They use propellants (like hydrocarbons or compressed... Continue reading "Pharmaceutical Dosage Forms: Creams, Powders, and Solutions" »