CH3—Matter: Phases, Equilibrium, Properties & Chemical Change

Phases of Matter

• Traditional teaching: 3 phases (gas, liquid, solid) experienced on Earth under “normal” T & P.
• Reality: 8 total phases (mention only briefly; higher‐energy/pressure forms include plasma, quark–gluon etc.).
  • Plasma: atoms stripped of e⁻ under very high T/P.
  • Beyond plasma: nuclei themselves can be disassembled at extreme conditions.
  → These exotic phases are not encountered in everyday terrestrial conditions, so the course focuses on gas, liquid, solid.
• Particle-motion hierarchy (average speeds): v{gas} > v{liquid} > v_{solid} but velocity distribution is Gaussian ⇒ not all particles in a phase move at the same speed.
• Interface = physical boundary separating two phases.

Spontaneous Phase Changes at Constant T

• Because of velocity distribution, individual collisions can move a particle across the interface without changing the bulk temperature.
  • Fast-moving surface molecules in a liquid can escape → evaporation.
  • Slow-moving gas molecules hitting liquid surface can lose E and stick → condensation.

Closed-Bottle Water Example → Dynamic Equilibrium

• Requirements: closed system (no mass exchange with surroundings).
• Competing processes:
  • Liquid → gas via high-energy collisions (evaporation).
  • Gas → liquid when low-energy gas collides with surface (condensation).
• Dynamic equilibrium: rate(evaporation) = rate(condensation).
  • Macroscopically, amount of liquid & vapor appears constant even though micro‐scale change is continuous.

Physical vs. Chemical Properties & Changes

Definitions

• Property: a feature that describes every particle of a substance.
• Physical Property/Change: identity of particles remains the same; involves phase or arrangement only.
  Examples: malleability, hardness, color, luster, melting/freezing/boiling points, solubility (spreading of solute in solvent’s sphere of hydration).
• Chemical Property/Change: involves formation of new substances; look for reaction verbs (combustion, oxidation‐reduction, synthesis, decomposition, etc.).

Four Observable Signs of a Chemical Reaction (in lab)

1. Color change (must accompany formation of new material; painting ≠ chemical change).
2. Gas evolved (bubbling not due to pre-dissolved gases).
3. Precipitate formed (solid appears when mixing solutions).
4. Heat exchange (temperature change felt or measured):
   • Exothermic: releases heat.
   • Endothermic: absorbs heat.

Everyday Chemical Change Vocabulary

• Rusting: oxidation of Fe; orange‐brown Fe₂O₃•xH₂O coating.
• Tarnishing: oxidation of Ag; dull gray Ag₂S layer on silverware.
• Corrosion: acid attacking metals (common around battery terminals).
• Souring/Denaturing of Food: structural change in proteins (e.g., milk spoiling).

Extensive vs. Intensive Properties

Classification Logic

• Can apply to both physical and chemical properties.
• Extensive: value depends on amount of substance.
  • Mass $m$, volume $V$, length $L$, total charge, total heat $q$, etc.
• Intensive: value depends on identity of substance, independent of sample size.
  • Density $\rho$, melting point $T<em>m$, conductivity $\sigma$, specific heat $c</em>p$, etc.

Illustrative Examples

• Mass of Cu sample doubles when number of Cu atoms doubles → extensive.
• Length of Cu wire proportional to atoms present → extensive.
• Density of water at $25\,^{\circ}\text{C}$ is $\approx 1.00\,\text{g mL}^{-1}$ whether glass, bucket, or pool → intensive.
• (Approx.) density of a generic metal X: $\rho \approx 8.6\,\text{g mL}^{-1}$ (instructor unsure of exact Cu value, so labels it metal X).

Study & Course Logistics Mentioned

• Chapter 3 (matter & energy) is content-heavy; historically split into two tests.
• Summer schedule combines Ch. 3 & 17 (and 20) into one large assessment.
• Students are encouraged to pause video, copy provided notes, and review practice test resources.

Conceptual & Real-World Connections

• Gaussian velocity distribution links statistical mechanics to observable phase behaviors (evaporation without bulk heating).
• Dynamic equilibrium underlies everyday phenomena (sealed soda equilibrium CO₂(aq) ⇌ CO₂(g)).
• Intensive/extensive framework vital for thermodynamics (state functions vs. path functions; scaling laws).
• Chemical reaction indicators help in industrial safety (detecting leaks, spoilage) and laboratory diagnostics.

Ethical & Practical Implications

• Understanding phase behavior crucial for safe pressurised container design (e.g., aerosol cans, autoclaves).
• Recognizing chemical vs. physical changes aids environmental decisions (e.g., painting ≠ hazardous waste, corrosion control on infrastructure).
• Awareness of chemical spoiling (souring milk) impacts food safety and waste reduction.

Key Numeric / Scientific Data Recap

• v{gas} > v{liquid} > v_{solid} (qualitative hierarchy).
• Water density at room T: $\rho<em>{H</em>2O} \approx 1.00\,\text{g mL}^{-1}$.
• Example metal density: $\rho_{X} \approx 8.6\,\text{g mL}^{-1}$.
• Four signs of chemical reaction enumerated (color, gas, precipitate, heat).

Use these structured notes as a standalone reference for Chapter 3 content on matter phases, properties, and chemical vs. physical distinctions.