Viscosity, Surface Tension & Intermolecular Forces

• Viscosity is a liquid's resistance to flow freely.
• A liquid's viscosity relates to its intermolecular force, which determines how easily molecules move.
• Larger molecules typically have higher viscosity.
• Viscosity and heat are inversely proportional.
• Viscosity and the strength of intermolecular forces are directly proportional.
• Surface tension is the energy required to expand a liquid surface.
• Liquids with stronger intermolecular forces have higher surface tension.
• Surface tension allows objects with a higher density than water to float on the surface of water.

Intermolecular Forces

• Intermolecular forces mediate interactions between molecules.
• They are electrostatic forces of attraction between molecules in a compound.
• These forces attract molecules, bring them closer, and stabilize the compound.
• Cohesive forces are intermolecular forces between molecules of a liquid, describing the attraction between comparable molecules.
• Adhesive forces describe interactions between a liquid and a solid surface; a liquid clings to the surface it rests on with wetting agents.
• Capillary action moves water molecules against gravity, which is important for plant life.
• Dipole-dipole forces are attractive forces between the positive end of one polar molecule and the negative end of another.
• Ion-dipole forces are attractive forces between an ion and a neutral molecule with a dipole.
• Van der Waals forces are weak intermolecular forces dependent on the distance between atoms or molecules, that arise from interactions between uncharged atoms/molecules.

Phase Changes

• Enthalpy: total heat content of a system, equaling the internal energy plus the product of pressure and volume.
• Condensation: the change of state from gas to liquid, which can be achieved by cooling or saturating the air.
• Vaporization: a phase transition from liquid to vapor, or the physical destruction of an object via intense heating.

Vaporization vs. Evaporation

• Vaporization occurs when a liquid changes to its vapors at its boiling point; evaporation occurs below the boiling point.
• Vaporization happens at a fixed temperature (boiling point); evaporation can occur at various temperatures.
• Temperature remains constant during vaporization but may change during evaporation.
• Vaporization is a fast, violent process; evaporation is slow and silent.
• Vaporization occurs throughout the liquid's mass, whereas evaporation happens only at the surface.
• Melting is the process where a substance changes from solid to liquid, requiring energy transfer.
• Freezing is when a liquid turns into a solid as its temperature drops below its freezing point.
• Sublimation converts a substance directly from solid to gas, skipping the liquid phase.

Solids

• Crystalline solids (true solids) are uniform with long-order arrangements and anisotropic force. Light bounces in these solids, resulting in different light speeds in different directions.
• Amorphous solids (false/pseudo/super-cooled solids) are non-uniform with short-order arrangements and isotropic force. Light passes through these solids, at the same speed in all directions.

Types of Crystalline Solids

• Conductors allow electricity to flow freely, while insulators hinder this flow.

Characteristics of Crystalline Solids

• Ionic solids have high melting points, are hard and brittle, and are insulators in solid form but conductors when liquid.
• Metallic solids have high melting points, are malleable and ductile, and are good conductors.
• Covalent solids have high melting points, are hard, and are poor/semi-conductors.
• Molecular solids have low melting points, are soft, and are insulators.

Solutions

• A solution is a homogeneous mixture of two or more substances.
• A solute is present in a smaller amount in a solution, and its dissolving process is solvation or dissolution.
• A solvent dissolves a solute to form a solution; solvents can be liquids, gases, or solids.
• Concentrated solutions contain large quantities of solute per unit amount of solution, with solute greater than solvent.
• Dilute solutions contain small quantities of solute per unit amount of solution, with solute less than solvent.
• Solubility measures how much solute dissolves in a solvent at a given temperature.
• A saturated solution has a concentration at the solubility limit, while an unsaturated solution is below this limit.

Energy

• Energy is the capacity to do work.
• Kinetic energy is the energy of motion.
• Potential energy is energy at rest.
• The first law of thermodynamics states that energy can neither be created nor destroyed, only transferred. The total energy of the universe is constant.
• Heat is the energy transfer when two samples at different temperatures are in contact. Energy transfers from hotter to colder samples until they reach thermal equilibrium.
• Solution concentration indicates the amount of solute in a given amount of solution or solvent.
• The amount of solute is in the numerator (grams or moles), and the quantity of solvent or solution is in the denominator (mass or volume).
• % Mass = (Mass of Solute / Mass of Solution) x 100

Molarity

• Molarity (M) measures the solute per liter of solution.
• The amount of solute is proportional to the volume, and molarity is the proportional constant.
• Moles = Mass of Solute / Molar Mass of Solute
• Mass of solute = Moles of solute × Molar mass
• Volume = Moles of Solute / Molarity

Molality

• Molality (m) is the number of moles of solute dissolved in 1 kg of solvent.
• m = moles of solute / kilograms of solvent

Dilution

• Concentrated solutions are diluted to a lower concentration by adding more solvent.
• M1V1 = M2V2