1.1.3Additional lessons
Changes of State — IB Chemistry HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 2 of 172
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 4Names of the Changes
Each change of state involves a change in the arrangement and energy of the particles.
Melting
- Melting Solid to liquid, endothermic, as particles gain enough energy to leave fixed lattice positions.
Freezing
- Freezing Liquid to solid, exothermic, as particles lose energy and settle into fixed positions.
Vaporisation
- Vaporisation Liquid to gas, endothermic, as particles gain enough energy to overcome the forces between them.
Condensation
- Condensation Gas to liquid, exothermic, as particles slow down and attractive forces pull them close together.
Section 2 of 4Sublimation and Deposition
Sublimation and Deposition
Sublimation
- Sublimation Solid goes directly to gas without becoming liquid, as shown by iodine and solid carbon dioxide at normal pressure.
Deposition
- Deposition Gas goes directly to solid, as when water vapour forms frost on a cold surface.
Evaporation
- Evaporation Occurs below the boiling point at the surface of a liquid, when the fastest particles escape.
Boiling
- Boiling Occurs at the boiling point throughout the liquid, where bubbles of vapour form inside it.
Section 3 of 4Heating Curve
When a solid is heated steadily the temperature changes in stages.
1
In the solid region the temperature rises because the energy supplied increases the average kinetic energy of the vibrating particles.
2
At the melting point the temperature stays constant as the energy supplied overcomes attractions between particles.
3
In the liquid region the temperature rises again as the average kinetic energy increases.
4
At the boiling point the temperature stays constant again while the liquid becomes a gas.
5
In the gas region the temperature rises further as the gas particles gain kinetic energy.
Section 4 of 4Exam Checklist & Tips
1.1.3 – Key Points for the Exam
- Melting point The temperature at which a pure solid changes to a liquid.
- Sublimation The change of state from solid directly to gas.
- Endothermic A change that takes in energy from the surroundings.
- Exothermic A change that releases energy to the surroundings.
Common Mistakes
- Stating that the temperature rises during a change of state; it stays constant.
- Saying that energy goes into increasing kinetic energy at the melting point, when it goes into overcoming attractions.
- Confusing evaporation, which is at the surface, with boiling, which is throughout the liquid.
- Thinking that bonds within molecules break when a molecular substance boils.
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