4.3.4Additional lessons
Carbon Dioxide Levels and the Greenhouse Effect — IB Chemistry HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 82 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 4How the Greenhouse Effect Works
The natural greenhouse effect keeps Earth warm enough for liquid water.
Incoming radiation
- Incoming radiation The Sun emits mostly visible and ultraviolet light, which passes through the atmosphere and warms Earth's surface.
Outgoing radiation
- Outgoing radiation The warm surface re-emits energy as longer-wavelength infrared radiation toward space.
Absorption
- Absorption Greenhouse gases absorb some of this infrared radiation because it matches the frequencies of their bond vibrations.
Re-emission
- Re-emission The molecules re-emit the energy in all directions, so part of it returns to the surface and warms the lower atmosphere.
Section 2 of 4Why Some Gases Absorb Infrared
Why Some Gases Absorb Infrared
Bond vibration
- Bond vibration Bonds stretch and bend at set frequencies, and absorption occurs when infrared matches one of them.
Dipole change
- Dipole change Absorption needs a vibration that changes the molecule's dipole moment, as with CO₂, CH₄ and H₂O.
Non-absorbers
- Non-absorbers N₂ and O₂ have no dipole change on stretching, so they do not absorb infrared significantly.
Greenhouse gases
- Greenhouse gases Water vapour, carbon dioxide, methane and dinitrogen monoxide are major examples.
Section 3 of 4Enhanced Greenhouse Effect
The distinction between the natural and the enhanced effect is a frequent exam point.
1
Burning fossil fuels returns carbon stored for millions of years to the atmosphere as CO₂.
2
Deforestation removes trees that would have absorbed CO₂ by photosynthesis.
3
Higher CO₂ concentration traps more outgoing infrared radiation and raises average temperatures.
4
Warming causes ice melt, sea-level rise, changing rainfall and more extreme weather in many regions.
5
Oceans absorb extra CO₂, forming carbonic acid and slowly lowering the pH, which harms shell-forming organisms.
Section 4 of 4Exam Checklist & Tips
4.3.4 – Key Points for the Exam
- Greenhouse gas A gas that absorbs infrared radiation from Earth and re-emits it.
- Infrared radiation Electromagnetic radiation with wavelengths longer than visible light, emitted by warm surfaces.
- Enhanced greenhouse effect Additional warming due to human-produced greenhouse gases.
- Ocean acidification The decrease in ocean pH as dissolved CO₂ forms an acid.
Common Mistakes
- Confusing the greenhouse effect with the ozone layer problem, which involves ultraviolet radiation.
- Saying greenhouse gases reflect heat like a mirror rather than absorbing and re-emitting infrared.
- Stating that N₂ and O₂ are the main greenhouse gases because they are most abundant.
- Claiming that CO₂ is the only greenhouse gas, ignoring methane and water vapour.
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