Matter exists in three principal states — solid, liquid, and gas — governed by the balance between two competing factors:

1. Kinetic energy (molecular motion) — tends to disorder and separate molecules
2. Intermolecular forces (attractions) — tend to hold molecules together

When kinetic energy dominates: gas state. When intermolecular forces dominate: solid state. Liquid is intermediate.

Three fundamental questions this chapter answers:

• How do ideal gases behave under changing conditions? (Gas Laws)
• How fast do gas molecules actually move? (Kinetic Molecular Theory)
• Why do real gases deviate from ideal behavior? (Van der Waals equation)

NEET Relevance: 1-2 questions per year. Key focus areas:

• Numerical problems using PV = nRT
• Graham's Law calculations (molar mass from diffusion rates)
• Molecular speed ordering and formulas
• Interpreting Z vs P graphs for real gases