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

Thermal Energy and Particle Motion

Thermal energy is intrinsically linked to temperature, which reflects the movement of particles within matter. This concept is a cornerstone of the Kinetic Theory of Matter, stating that all matter is composed of tiny particles in constant, random motion.

Changes in Matter: Physical vs. Chemical

When we observe the world around us, we identify two distinct types of transformations that matter undergoes:

Physical Changes

A physical change is a process where the fundamental nature or chemical composition of a substance remains unaltered. The original substance does not transform into a new, chemically different substance. Examples include:

• Changes of State: Such as ice melting into water, or water boiling into steam.

Mixtures and Compounds

A mixture is a material system made up of two or more different substances which are mixed but not combined chemically.

Types of Mixtures

• Heterogeneous: The components are visibly diverse.
• Homogeneous: The components are uniformly distributed, appearing as a single substance.

Basic Chemical Concepts

• Phase: A physically distinct form of matter, such as a solid, liquid, or gas.
• Element: A substance that is made up of only one type of atom.

Changes of State

• Melting Point: The temperature at which a solid melts. The particles gain energy, vibrate faster, and eventually move around, becoming a liquid.
• Boiling Point: The temperature at which a liquid boils. The particles gain energy, move faster, break free, and become a gas.

Tests for

Understanding Temperature

What is Temperature?

Temperature is the measurement of a substance's thermal energy.

Measuring Temperature

Mercury Thermometer

A mercury thermometer consists of a bulb containing liquid mercury and a thin tube. The liquid expands due to thermal expansion and rises up the tube, allowing the temperature to be read on a calibrated scale.

Digital Thermometer

A digital thermometer uses a microprocessor that measures the temperature and displays it on a liquid crystal display (LCD).

Temperature Scales

Common temperature scales include Celsius (ºC) and Kelvin (ºK).

• Celsius to Kelvin: K = C + 273.15
• Kelvin to Celsius: C = K - 273.15

Heat Transfer Mechanisms

Conduction

Conduction is the transfer of heat energy primarily from solid to solid... Continue reading "Science Essentials: Temperature, Heat, Reactions, Environment" »

An Arrhenius acid is a substance that dissociates in water to form hydrogen ions or protons. In other words, it increases the number of H⁺ ions in the water. In contrast, an Arrhenius base dissociates in water to form hydroxide ions, OH^-.

A Bronsted-Lowry acid is a solution that donates protons and is known as a proton donor. The Bronsted-Lowry base, on the other hand, is a solution that accepts protons and is known as a proton acceptor. Going back to a Bronsted-Lowry acid, in general, it must contain a hydrogen ion that it can give up.

Defining Matter

Matter is defined as anything that has mass and takes up space.

Pure Substances

Pure substances possess constant physical properties (e.g., odor, hardness, density, boiling points). They can be classified as either elements or compounds.

Elements

Elements consist of only one kind of atom and cannot be broken down into a simpler type of matter by either physical or chemical means. Elements are found in the periodic table and are categorized as:

• Metals: Tend to lose electrons, resulting in a positive charge (cations).
• Nonmetals: Tend to gain electrons, resulting in a negative charge (anions).
• Metalloids.

Compounds

Compounds are formed when atoms of two or more different elements are chemically bound together. They can be broken down into... Continue reading "Classification of Matter: Elements, Compounds, and Separation Techniques" »

Advanced Materials Science Concepts

High Entropy Alloys (HEAs)

What Materials Are Named ‘High Entropy Alloys’?

Substances constructed with equal or nearly equal quantities of five or more metals. They exhibit a higher degree of fracture resistance, tensile strength, as well as corrosion and oxidation resistance compared to conventional alloys.

What Conditions Must Be Satisfied to Obtain HEA from a Number of Chemical Elements?

Gibb’s phase rule applies: F=C-P+2.

Graphene and Graphene-Like Materials

Differences Between Graphene and Silicene

Silicene is not flat; it is stronger than graphene. Silicene’s hydrogenation reaction is more exothermic than graphene’s.

Three Examples of Graphene-Like Materials

• Layered van der Waals materials
• Graphene-like

Biotic and Abiotic Factors in an Ecosystem

• Chemistry: The study of matter.
• Matter: Any substance that has mass and takes up space.
• Energy: The capacity of a physical system to do work.
• Ecosystem: All of the living things in a given area.
• Biotic: Living organisms (e.g., flowers, plants, bacteria).
• Abiotic: Non-living organisms (e.g., water, soil, air, light, wind).

States of Matter

• Solids: More dense, particles are very close, molecules only vibrate, cannot flow, defined shape, defined volume, not compressible.
• Liquids: Dense, particles are close, molecules have random flow, can flow, adaptable shape, defined volume, very little compressible.
• Gas: Less dense, particles are separated, molecules have a random, fast, and free movement, can flow, no shape,

HOW DO ATOMS BEHAVE DURING A CHEMICAL REACTION?

Chemical reactions occur when bonds between atoms break and new bonds form, creating a new arrangement of atoms and at least one new substance. Observable changes, such as temperature fluctuations, color changes, gas formation, new solids, and odors, accompany these reactions.

Conservation in Chemical Reactions

Besides energy, mass is also conserved during chemical reactions. Lavoisier's experiment disproving the "phlogiston theory" led to the development of the "law of conservation of mass," which states that matter cannot be created or destroyed in a chemical reaction. Balanced chemical equations represent this law.

Energy and Reactions

Energy is required to initiate reactions. Simply mixing chemicals... Continue reading "Understanding Chemical Reactions: From Atoms to Acid Rain" »

Thompson

Thompson was an historian with a Marxist background, whose interests of radical political works set him apart from other authors we studied. He, as Hoggart, followed culturalism, a perspective that stresses human agency, or the active production of culture, and not its passive consumption. His book The Making of the English Working Class embodies this term, since in it he traces the development of the English Working Class between the years 1780 and 1832, more or less the time encompassed by the Industrial Revolution. The book can be seen as a rescue operation of the members (especially radical ones) of the working class lost in the history lead by the deeds of monarchs, statesmen, military leaders and politicians. These other histories... Continue reading "The Making of the English Working Class: A Radical Perspective" »