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Chapter 8. States of Matter

Recommended Article : 【Chemistry】 Table of Contents


1. States of Matter

2. Changes of State

3. Phase Diagram



1. States of Matter

⑴ States of Matter : Generally classified into three categories. A fourth state also exists.

Gas

Liquid

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.

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

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

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