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

Chemical Reaction Rates: Fundamentals and Catalysis

Key Concepts in Chemical Kinetics

• Rate Law

  The speed of a reaction is directly proportional to the concentrations of the reactants raised to some exponent.

• Collision Theory

  This theory states that a greater concentration of reactants leads to more frequent collisions, thereby increasing the reaction rate.

• Reaction Profile

  A diagram that illustrates the progress or development of a chemical reaction.

Factors Influencing Chemical Reaction Rates

The speed of a chemical reaction depends on several critical factors:

• Nature of Reactants: The inherent properties of the reacting substances.
• Concentration: Higher concentrations generally lead to faster reactions.
• Physical State of Reactants: This factor involves

Vowel Phonemes

Vowel phonemes are speech sounds produced with an open vocal tract, allowing air to flow freely. They are classified by tongue position (front, central, back), tongue height (high, mid, low), and lip rounding.

• /i/: Front, high, unrounded (e.g., as in "feet")
• /e/: Front, mid, unrounded (e.g., as in "bed")
• /a/: Central, low, unrounded (e.g., as in "father")
• /o/: Back, mid, rounded (e.g., as in "boat")
• /u/: Back, high, rounded (e.g., as in "boot")

Consonant Phoneme Allographs

A single phoneme (distinct sound unit) can have different spellings (graphemes or allographs) depending on the context or language:

• /b/: b, v, w (e.g., ball, van, wear – depending on language and pronunciation)
• /s/: z (e.g., zoo), c (before e, i; e.g., city)
• /k/: c

Foundational Atomic Theory and Discoveries

John Dalton (1808)

Dalton proposed that matter consists of indivisible particles called atoms. His model (sometimes historically referenced as the "fruitcake" model) established key principles:

• Atoms of the same element are identical in mass and properties.
• Atoms combine to form compounds and are not destroyed or created, only rearranged (involving the rearrangement of electrons).

Key Discoveries in Atomic Structure

• Michael Faraday (1833): Experiments proposed the relationship between electricity and atoms (electrolysis).
• J.J. Thomson: Studied electrical conductivity in gases using discharge tubes.
• Eugen Goldstein: Used a cathode ray tube to describe protons.
• Henri Becquerel (1896): Accidentally discovered

1. 1. Specific Volume and Critical Conditions

   Statement: The specific volume of a gas is the volume that would occupy 1 mole of that gas at its critical temperature and pressure. (False)

   Correction and Explanation:

   This statement is false. The critical volume is the volume occupied by one mole of a substance at its critical point. Specific volume, by definition, is the volume per unit mass of a substance. The original statement incorrectly defines specific volume in terms of molar volume at critical conditions.

2. 2. Adiabatic Processes and Heat Transfer

   Statement: When there is heat loss to the environment, a process cannot be adiabatic. (True)

   Explanation:

   An adiabatic process is fundamentally defined by the absence of heat transfer (Q=0) to or from the

Fundamental Concepts of Atomic Structure

The Bohr Atomic Model and Energy Levels

The Bohr atom only allows electrons to move in certain, quantized orbits around the nucleus. The lowest energy level corresponds to the orbit closest to the nucleus. As the orbit moves away from the core, the energy levels increase.

Hydrogen Spectra Explanation

The interaction of electrons with energy explains the hydrogen spectra:

• The electron absorbs energy when moving from a lower energy level to a higher energy level.
• When passing from a higher level to a lower level, the electron emits energy in the form of radiation (a photon).
• The energy absorbed or emitted by the photon equals the energy difference between the levels.
• The frequency of the emitted or absorbed radiation

Key Concepts in Metallurgy and Materials Science

• The higher the ideal critical diameter of steel, the lower its hardenability.
• The greater the hardenability of steel, the greater the hardness of martensite that forms upon quenching.
• The lower the specific heat of a bath, the more energetic the cooling it produces during tempering.
• Examples of transformations include diffusion and martensitic transformations.
• Standard heat treatment can result in a coarser grain size in steels compared to those annealed at the same temperature.
• Hadfield steel, with more than 1% carbon and 14% manganese, is an example of martensitic steel.
• Magnesium is the element that causes the graphitization of white cast irons.
• Standard heat treatment produces a coarser grain size

Modelos atómicos: Thomson, Rutherford y Bohr

Thomson imaginó el átomo como una especie de área continua positiva en la que los electrones están incrustados, más o menos como pasas en un pudding. Este modelo de Thomson fue bastante razonable y fue aceptado durante varios años, ya que permitía explicar ciertos fenómenos.

Formación de iones

La explicación de la formación de iones es la siguiente: un átomo que ha ganado o perdido uno o más electrones se convierte en un ion. Los electrones pueden perderse o ganarse con relativa facilidad, de modo que su número puede variar dentro del átomo, mientras que el número de protones se mantiene siempre fijo para cada átomo.

Un átomo que pierde electrones se convierte en un ion positivo o... Continue reading "Evolution of Atomic Models: Thomson to Bohr" »

Fundamental Chemical Definitions

Molecule

The union of atoms.

Lattice

A continuous structure of millions of atoms.

Chemical Bond

The attractive force that keeps atoms united in a molecule or a crystal.

Elementary Chemical Substance

Atoms of the same element that unite.

Chemical Compound

Atoms of different elements that unite.

The Octet Rule

Atoms of different chemical elements tend to join with other atoms to have eight electrons in their outermost shell, known as an octet, to achieve greater stability.

Types of Chemical Bonds

Ionic Bond

The transfer of valence electrons. The ionic bond is the union of oppositely charged ions through electrostatic forces of attraction. In this case, the elements bond to achieve a noble gas electron configuration.

Ionic Crystal

A... Continue reading "Chemical Bonding and Material Attributes" »

Substances, Mixtures, and Separation Techniques

1. Pure Substances vs. Mixtures

• Distilled Water: Pure substance/compound
• Tap Water: Mixture/homogeneous
• Diamond: Pure substance/element
• Gasoline: Mixture/homogeneous
• Wine: Mixture/homogeneous
• Air: Mixture/homogeneous

2. Dalton's Theory

• Matter is made up of indivisible and indestructible atoms.
• All atoms of the same element are equal in mass and properties.
• Compounds are formed by the combination of different elements.

3. Separation Techniques

• Screening: Separates solid particles of different sizes. Instrument: sieve.
• Filtration: Separates solids from liquids. Instrument: filter.
• Evaporation: Separates solids from liquids when the liquid is not needed. Works best with homogeneous mixtures. The process is faster

Aluminum

Aluminum is used in telescopes. Tempered powder paint is used in metal protection and the preparation of alloys. Aluminum forms alloys with other metals. Duralumin, an aluminum alloy, is used in aeronautics because it is very lightweight and has great resistance.

Aluminothermy

Aluminothermy is a metal extraction procedure that reduces metal oxides using aluminum powder. Metals such as chromium, manganese, and molybdenum are obtained using this method.

Salts of Aluminum

Important industrial salts are called alum (double salts).

Natural Aluminum

Aluminum is not found free in the Earth's crust. It is named after these characteristics:

1. Alumina
2. Hydroxide
3. Silicates

Obtaining Aluminum

Aluminum is extracted using the electrolytic method. Bauxite and cryolite... Continue reading "Aluminum, Copper, Polymers, and Ceramics: Properties and Uses" »