Water and Its Properties

Chemical Equilibrium and Polar Molecules

Chemical equilibrium occurs when the rate of the forward reaction equals the rate of the reverse reaction, resulting in no net change in the concentration of reactants and products. Polar molecules have an uneven distribution of electrical charge, leading to partial positive and negative regions within the molecule.

• Chemical Equilibrium: The state in which the concentrations of reactants and products remain constant over time.

• Polar Molecule: A molecule with an uneven distribution of charges (e.g., water).

Cohesion, Adhesion, and Surface Tension

Water exhibits unique properties due to hydrogen bonding, including cohesion, adhesion, and surface tension.

• Cohesion: The attraction between molecules of the same substance (e.g., water molecules stick together).

• Adhesion: The attraction between molecules of different substances (e.g., water and glass).

• Surface Tension: A measure of how difficult it is to stretch or break the surface of a liquid due to cohesive forces.

Kinetic Energy, Temperature, and Heat

Kinetic energy is the energy of motion, and temperature measures the average kinetic energy of molecules. Heat is the transfer of thermal energy from one body to another.

• Kinetic Energy: Energy of motion of atoms and molecules.

• Temperature: Average kinetic energy of molecules in a body of matter.

• Heat: Thermal energy transferred from one body to another.

• Calorie: The amount of heat required to raise the temperature of 1 g of water by 1°C.

Specific Heat and Heat of Vaporization

Water has a high specific heat and heat of vaporization, which helps moderate Earth's climate and organisms' internal temperatures.

• Specific Heat: The amount of heat required to change the temperature of 1 g of a substance by 1°C.

• Heat of Vaporization: The quantity of heat a liquid must absorb for 1 g to be converted to gas.

Equation:

• Evaporative Cooling: As liquid evaporates, the surface cools down, helping organisms avoid overheating.

Water: The Solvent of Life

Solutions, Solvents, and Solutes

Water is known as the universal solvent due to its ability to dissolve many substances.

• Solution: A homogeneous mixture of two or more substances.

• Solvent: The dissolving agent (e.g., water).

• Solute: The substance that is dissolved.

• Aqueous Solution: A solution in which water is the solvent.

Hydration Shells and Hydrophilic/Hydrophobic Substances

• Hydration Shell: The sphere of water molecules surrounding each dissolved ion.

• Hydrophilic: Substances that have an affinity for water (e.g., salts, cellulose).

• Hydrophobic: Substances that do not have an affinity for water (e.g., oils, fats).

Acids, Bases, and pH

Acids and bases alter the concentration of hydrogen ions in a solution, affecting the pH.

• Acid: A substance that increases the hydrogen ion concentration in a solution.

• Base: A substance that reduces the hydrogen ion concentration (accepts H+).

• pH Scale: Measures the concentration of H+ ions in a solution.

Equation:

• Strong Acids/Bases: Completely dissociate in water (e.g., HCl, NaOH).

• Weak Acids/Bases: Partially dissociate (e.g., ammonia).

Buffers

Buffers help maintain a stable pH in biological systems by minimizing changes in H+ and OH- concentrations.

• Buffer: A substance that minimizes changes in the concentration of H+ and OH- in a solution.

• Most solutions contain a weak acid and its corresponding base (e.g., H2CO3 in blood).

Carbon and the Molecular Diversity of Life

Carbon: The Backbone of Biological Molecules

Carbon atoms can form four covalent bonds, allowing for a diversity of stable organic molecules.

• Organic Compounds: Carbon-based compounds.

• Macromolecules: Large molecules composed of thousands of covalently connected atoms (e.g., carbohydrates, proteins, nucleic acids, lipids).

Classes of Biological Macromolecules

• Carbohydrates: Provide energy and structural support (e.g., starch, glucose).

• Proteins: Perform a wide range of functions, including catalysis (enzymes), structure, and transport.

• Nucleic Acids: Store and transmit genetic information (e.g., DNA, RNA).

• Lipids: Diverse group of hydrophobic molecules, not true polymers (e.g., fats, phospholipids).

Isomers and Functional Groups

Isomers are compounds with the same molecular formula but different structures and properties. Functional groups are specific groups of atoms attached to carbon skeletons that participate in chemical reactions.

• Structural Isomers: Differ in the covalent arrangement of atoms.

• Cis-Trans Isomers: Differ in spatial arrangement due to inflexibility of double bonds.

• Enantiomers: Mirror images of each other due to asymmetric carbon.

Macromolecules: Structure and Function

Monomers and Polymers

Macromolecules are polymers built from monomers. Monomers are small, repeating units that serve as the building blocks of polymers.

• Polymer: Long molecule consisting of many similar or identical building blocks linked by covalent bonds.

• Monomer: Single, repeating unit of a polymer.

• Enzymes: Specialized macromolecules (usually proteins) that speed up chemical reactions.

Dehydration and Hydrolysis Reactions

• Dehydration Reaction: Two monomers bond together through the loss of a water molecule.

• Hydrolysis: Polymers are disassembled to monomers by the addition of water.

Carbohydrates: Structure and Types

Carbohydrates are sugars and polymers of sugars. They serve as energy sources and structural materials.

• Monosaccharides: Simple sugars (e.g., glucose, fructose).

• Disaccharides: Double sugars, formed by joining two monosaccharides via a glycosidic bond (e.g., sucrose).

• Polysaccharides: Polymers of many monosaccharides joined by glycosidic linkages (e.g., starch, glycogen, cellulose).

Examples of Monosaccharides

Polysaccharides: Starch, Glycogen, and Cellulose

• Starch: Storage polysaccharide in plants, composed of glucose monomers (amylose and amylopectin).

• Glycogen: Storage polysaccharide in animals, highly branched.

• Cellulose: Structural polysaccharide in plant cell walls, composed of β-glucose monomers.

Additional info: Most animals cannot digest cellulose due to lack of appropriate enzymes; some microorganisms can.

Disaccharide Synthesis

Disaccharides are formed by dehydration reactions between two monosaccharides.

• Sucrose: Formed from glucose and fructose.

• Lactose: Formed from glucose and galactose.

• Maltose: Formed from two glucose units.