Kinetic Molecular Theory

Kinetic Molecular Theory of Matter

• Matter is composed of a large number of tiny particles such as molecules or ions
• These particles are in constant motion and possess kinetic energy
• Temperature is how we perceive this kinetic energy

Physical States and Temperature

• As temperature decreases, gas molecules can condense into liquids and then solids
• Slowly moving molecules are easily attracted to each other, resulting in condensed phases like liquids and solids
• Ionic compounds don't exist as gases because very high temperatures are needed to overcome the strong electrostatic attraction between their ions
• A compound's physical state is determined by its temperature, kinetic energy, and intermolecular forces

Gas State

• Molecules are in constant motion based on the Kinetics Molecular Theory of Matter and the Theory of Heat
• Molecular motion ceases only at absolute zero (0 K).
• High kinetic energy in a gas surpasses intermolecular attractive forces
• Gases spread to fill the volume of their container

Kinetic Theory Assumptions for Ideal Gases

• Gases consist of numerous molecules moving randomly in straight lines
• Volume of the molecules is negligible
• Intermolecular attraction is negligible
• Collisions are elastic with negligible collision time compared to the time between collisions
• Average kinetic energy is proportional to temperature T (in Kelvin)

Liquid State

• Liquid molecules move more slowly, rolling over each other
• When a gas cools, molecules slow down, and intermolecular forces become significant
• Mild binding forces hold the material together as a liquid
• Liquids consist of closely packed particles in continuous, random motion while maintaining volume
• Liquid volume depends on particle size and affects liquid properties
• Slower motion and lower kinetic energy allows intermolecular forces to influence liquid properties
• Liquids have fixed volume but take the shape of their container due to gravity

Terms Related to Liquids

• Evaporation: The process of a liquid changing to vapor below its boiling point
• Vapor pressure: The pressure exerted by a vapor in equilibrium with its liquid
• Vapor pressure depends on the nature of the liquid
• Vapor pressure increases as temperature increases
• Heat of vaporization: The change in enthalpy when a liquid changes into vapor or vice versa
• Molar heat of vaporization: The energy needed to change one mole of a substance into vapor

Solid State

• Molecules in solids can only vibrate
• When a liquid is cooled sufficiently, its molecules slow down so much that they become fixed in the structure of a solid
• Instead of moving around, the particles vibrate in place
• Solids consist of closely packed particles vibrating in fixed locations while maintaining a fixed volume and shape
• Solid volume depends on the size of particles
• Intermolecular forces have a stronger effect on solid properties because of the slow vibrations and minimal kinetic energy of the particles
• Solids have fixed volume and shape and gravity pulls them to the bottom of the container

Empirical Gas Laws

• Boyle's Law: Pressure-Volume relationship V ∝ 1/P (inverse relationship)
• Temperature volume is related

Ideal Gas Law

• An ideal gas is characterized by absolute pressure (P), volume (V), and absolute temperature (T)

The Ideal Gas Law Formula

• PV=nRT

Ideal Gas Conditions

• An ideal gas lacks intermolecular or interatomic forces like hydrogen bonding, dipole-dipole attraction, and London dispersion forces
• A real system approaches ideal gas behavior when pressure is extremely low and temperature is high enough to overcome intermolecular forces