Chapter 8. States of Matter
Recommended Article : 【Chemistry】 Table of Contents
1. States of Matter
⑴ States of Matter : Generally classified into three categories. A fourth state also exists.
① Gas
② Liquid
③ Solid
④ Plasma State
○ Definition : A mixture of ionized atoms or molecules in significant quantities, electrically neutral and conductive.
○ Typically formed during gas discharge.
○ Fourth state (e.g., fire, lightning). Ions flow like a fluid in high-temperature conditions.
○ Makes up 99% of the universe.
○ Used in semiconductors, LCDs, plasma display panels (PDP), nuclear fusion technology.
⑵ Critical Points
① Critical Temperature
○ Definition : The maximum temperature at which a liquid can exist.
○ The starting temperature for the fourth state, plasma state.
○ Above this temperature, all kinetic energy is greater than the maximum intermolecular force (considering repulsion), so it can no longer be considered a fluid.
○ Critical temperature of carbon dioxide is 31°C → Reason why a fire extinguisher makes sound in winter but not in summer.
② Supercritical Fluid
○ Definition : State of matter at temperatures and pressures above the critical point.
○ Density higher than gas but not in a liquid state.
○ Exhibits properties of both gas (diffusivity) and liquid (solubility).
**2. Changes of State
⑴ Changes of State
① Melting, Vaporization
② Fusion, Solidification
③ Sublimation
④ Dissolution
○ Example 1: Decompression Sickness
○ Definition : Symptoms that can lead to death or other conditions when scuba divers ascend too quickly after diving.
○ Cause : Underwater pressure causes gases to dissolve in the bloodstream, which can come out of solution and form bubbles as the diver ascends.
○ Prevention 1: Ascend slowly at 10-20 m/min.
○ Prevention 2: Use specialized equipment.
⑵ Boiling Point
① Increase in Intermolecular Forces → Increase in Boiling Point
② Surface Area : Longer carbon chains and fewer substituents lead to increased intermolecular forces → higher boiling point.
③ Polarizability : Higher polarizability (larger atomic radius, larger surface area) leads to increased intermolecular forces → higher boiling point.
⑶ Freezing Point : Also known as the solidification point
① Increase in Intermolecular Forces → Higher Freezing Point
② Surface Area : Longer carbon chains and fewer substituents lead to increased intermolecular forces → higher freezing point.
③ Symmetry : Higher energy required to convert from solid to liquid due to better stacking in crystalline lattice because of symmetry.
○ Example : Trans fat
⑷ Heat Entry and Exit during Phase Changes
① Sensible Heat : Heat that causes a change in temperature.
② Latent Heat : Heat absorbed or released without a change in temperature during a state change.
③ Latent Heat of Water
○ Heat of Fusion = 80 kcal/kg
○ Heat of Vaporization = 539 kcal/kg
⑸ Gel-Sol Transition in Solids : Important in Polymer Synthesis
Figure 1. Content of PGA and Melting Point and Gel-Sol Transition Temperature
3. Phase Diagram
⑴ Phase Diagram of Water
Figure 2. Phase Diagram of Water
① Triple Point of Water : 0.009 ℃, 4.58 mmHg
① Solid-Liquid Slope : While most substances have a positive slope, water has a negative slope.
○ Tin with four phases exhibits a similar behavior.
○ Feature : Generally, an increase in pressure leads to an increase in melting point, but water’s melting point decreases with pressure.
○ Cause : Expansion during solidification.
② Water Density Comparison
○ Near 0 ℃, water has higher density than ice.
○ Sudden increase in density when ice transforms into water.
○ Around 4 ℃, the hexagonal crystal structure of ice has the maximum number of hexagons, resulting in maximum density.
③ Phase Equilibrium Diagram of Ice : Distorted hexagons → Increased density
⑵ Phase Diagram of Carbon
Figure 3. Phase Diagram of Carbon
① Carbon has four phases.
② Density Comparison : Diamond > Graphite > Liquid > Gas
⑶ Phase Diagram of Sulfur
Figure 4. Phase Diagram of Sulfur
⑷ Phase Diagram of Iron
Figure 5. Phase Diagram of Iron
Input: 2019.01.14 19:03
Modification: 2020.03.20 09:04