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

Phase Change Materials (PCM)

PCMs are substances that absorb or release heat during phase transitions, typically triggered by temperature changes. They store energy as latent heat.

Types of PCMs

• Organics (Paraffins, Fatty Acids): Characterized by high latent heat, chemical stability, and non-corrosive properties. They do not suffer from supercooling but exhibit low thermal conductivity and are flammable.
• Inorganics (Salts and Hydrates): Offer high thermal storage density and conductivity at a low cost. However, they are corrosive, chemically unstable, and often require subcooling to solidify.

Technical Note: PCMs absorb heat when melting and release it during solidification, effectively maintaining internal temperatures.

Corrosion Mechanisms and

Method 1: The Chemical Path

Δ_rH_m = Molar Enthalpy (kJ/mol)

Trigger: Only when a chemical reaction has taken place.

• ΔH_rxn = Enthalpy change of the whole reaction
• Δ_rH_m = Q_rxn / n
• Q_rxn = Heat of Reaction (kJ)

H₂O data: Mass or volume of water given. Chemical data: Mass, concentration, or moles of reactant burnt or dissolved.

Q_rxn = -Q_water

Note: If chemicals and water are involved in the reaction, flip the signs for Q_rxn and Q_water; if it is just warming, do not flip the signs.

Method 2: The Physical Phase Change Path

No chemical reaction; only temperature change or physical change occurs.

Scenario A: Changing Temperature (Substance stays same)

Q = mcΔT

• Units: Q (J or kJ) | m (g) | c (J/g·°C) | ΔT (°C)

Scenario B: Constant Temperature (Melting, boiling,

pure substance: is a phase of uniform composition and unchanging can not be decomposed into other substances of different classes by physical methods.

elements: they are pure substances that can not be decomposed into simpler ones through normal chemical processes.

compounds: they are pure substances made up of two or more elements, which can be decomposed by chemical methods on the elements of which are constituted. A compound always has the same elements and the same proportions regardless of the process followed.

Blended is an aggregation of different substances without causing any chemical reaction between them and therefore may be separated by physical methods.

ponderal laws: they refer to the quantity of matter of different substances... Continue reading "Laws ponderal" »

Organic Synthesis and Reaction Mechanisms

Malonic Ester Synthesis and Carbonyl Reactivity

Electrophiles (e+) for Malonic Ester Synthesis include epoxides, primary haloalkanes, and conjugated ketones. Esters react with 2 equivalents of irreversible nucleophiles, such as LiAlH4 and RMgBr, to yield an alcohol product. Acyl halides undergo fast hydrolysis and do not require a catalyst because the acyl halide is a better electrophile compared to carboxylic acids, and Cl- is a better leaving group than OH-.

Carbohydrate Chemistry

• Reducing sugars contain hemiacetals at the anomeric carbon.
• Alpha 1,4-linked polyglucans are known as amylose, used for energy storage in plants (digestible by humans).
• Oligosaccharides consist of 3-10 units.
• Reduction of monosaccharides

Aryl halide to diphenyl

Aryl halide reacts with sodium metal in the presence of dry ether to form diphenyl.

Name: Fittig reaction

Equations for SN1 step: tert‑butyl bromide to tert‑butyl alcohol

Equations for the step in SN1 of the conversion of tert‑butyl bromide into tert‑butyl alcohol.

IUPAC name for product from 2‑bromopentane with alcoholic KOH

IUPAC name for the major product obtained when 2‑bromopentane is heated with alcoholic KOH. Equation and name:

ANS: pent-2-ene

CH3-CH2-CH-CH3 ------> CH3-CH2-CH=CH-CH3

                     I

                   Br

NAME: elimination reaction

Why aryl halides are less reactive toward nucleophilic substitution

Aryl halides are less reactive towards nucleophilic... Continue reading "Key Organic Reactions: Fittig, Wurtz, Swarts, Kolbe‑Schmitt, Williamson" »

Hydrocarbon Classification and Properties

Chemical Categories

• Aliphatic: Chains/rings (Alkanes, Alkenes, Alkynes).
• Aromatic: Contains benzene ring.
• Derivatives: Organic. Atoms like O, N, halogens replace H.
• Inorganic: Oxides (CO₂, CO), Carbonates (CaCO₃, NaHCO₃), Carbides (CaC₂, SiC), Cyanides (NaCN).

Functional Groups

• Carboxylic Acid (-oic acid)

5. Describe what is electrodeposition, describe the different Experimental methods. Give examples. Advantages and disadvantages. It is the process of production a coating, usually Metallic, on a surface by the action of an electric current._Experimental Methods::-Electroplating: It is a plating process in which metal ions in a Solution are moved by an electric field to coat an electrode. Metallic cations From a solution are reduced on a conductive object (to form a thin layer).-Electrophoretic Deposition:Colloidal particles suspended in a liquid migrate under the Influence of an electric field (electrophoresis) and are deposited onto an Electrode._Advantages: uniform coating thicknen,easy control,high speed of Coating and high pucity._Disadvantages:

Challenges of Hydrogen Fuel Cells

The main issue with hydrogen fuel cells is that hydrogen is rarely found as a free element; it is usually found chemically combined with other elements, making it difficult to obtain.

• High cost: Due to this issue, producing, storing, and transporting hydrogen is expensive, and fuel-cell vehicles themselves cost more to make.
• Difficult storage: Hydrogen is very light and reactive, so it must be stored in strong tanks at very high pressures or extremely low temperatures, which is costly and complex. Its high reactivity means it can ignite easily, posing fire and explosion risks.
• Limited infrastructure: There are very few hydrogen refueling stations compared to gasoline or EV charging stations.
• Energy inefficiency:

Gas Chromatography Instrumentation and Analysis

1. Draw a block diagram of a GC instrument, labeling all the important components.

The components of a Gas Chromatography (GC) system follow this sequence:

• Mobile Phase Reservoir: Pressurized Helium (He) cylinder
• Sample Injector: Micro-syringe (located inside the oven)
• Stationary Phase: Column (located inside the oven)
• Detector: Thermal Conductivity Detector (TCD) or Flame Ionization Detector (FID)
• Readout: Computer system

2. What quantities are plotted on the x- and y-axes of (a) a chromatogram and (b) a calibration curve?

• a. Chromatogram: The x-axis represents time, and the y-axis represents the detector signal.
• b. Calibration Curve: The x-axis represents concentration, and the y-axis represents the peak

Fundamentals of Electrolysis

Electrolysis is the decomposition of a compound, in solution or in the molten state, brought about by the passage of electric current through it.

Definitions and Components

• An electrolyte is a substance in the molten state or as a solution in water, which allows the passage of electricity.
• A non-electrolyte is a substance in a solution that does not conduct electric current.
• A conductor is a substance which conducts or allows the passage of electricity.
• An insulator is a solid substance which does not conduct electricity.

Electrolysis Laws and Quantities

The amount of substance deposited or liberated is directly proportional to the quantity of electricity (Q) passed through the solution during electrolysis.

The moles of... Continue reading "Fundamentals of Electrolysis and Electrochemical Cells" »