States of Matter and Kinetic Molecular Theory

Study Notes

Matter exists in three primary states: solid, liquid, and gas.
The state of a substance depends on two factors: the forces holding particles together and the kinetic energy of particles (which tends to pull them apart).
Solids have a rigid, fixed shape and fixed volume; particles are in fixed positions and cannot move past each other. They cannot be squashed.
Liquids have a no fixed shape and fixed volume; particles are not held in fixed positions and can slide past each other. They cannot be squashed.
Gases have no fixed shape and no fixed volume; particles are not held in fixed positions and move freely in all directions. They can be squashed.

Attractive forces between particles determine the state of matter.
The weaker the attractive forces, the freer the particles are to move.
Intermolecular forces are crucial in determining the state of a substance.
Strong forces usually result in solids, while weaker forces typically lead to gases or liquids. Examples of forces include ionic, polar dipole-dipole, and dispersion forces.

All substances contain entities in constant random motion.
Robert Brown (1773-1858) observed this phenomenon in pollen under a microscope.
The constant motion of particles explains phenomena such as odors spreading through a room.
Particles in substances exhibit three types of motion: vibrational, rotational, and translational.
All particles vibrate, while rotation and translation only occur in liquids and gases respectively

Solids have vibrational motion and the strongest intermolecular forces, characterized by highly organized particles.
Liquids have vibrational, rotational, and translational motions, with intermediate intermolecular forces and an intermediate level of particle organization.
Gases have vibrational, rotational, and translational motions with weaker intermolecular forces and the least particle organization.

Temperature is a measure of the average kinetic energy of the entities in a substance.
Higher kinetic energy (higher temperature) means particles are more likely to overcome attractive forces and become gaseous.
Lower kinetic energy (lower temperature) results in particles being more likely to keep attractive forces, thus being liquid or solid.

The volume of individual gas molecules is negligible compared to the volume of the container.
There aren't attractive or repulsive forces between gas molecules.
Gas molecules move randomly in straight lines.
When gas molecules collide, there is no loss of kinetic energy.
The average kinetic energy of a gas is directly proportional to the temperature.

The Kinetic Molecular Theory (KMT) describes a hypothetical gas called an ideal gas. In an ideal gas, gas particles occupy little space and do not interact.
While no gas is perfectly ideal, the model is useful for calculating real gases' behavior under various conditions.