Theme B — The Particulate Nature of Matter
Theme B — The Particulate Nature of Matter — IB Physics SL Revision Notes & Topical Questions
5 min read 11 parts Lesson 1 of 44 Unit quiz
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.
Lesson summary
Theme B — The Particulate Nature of Matter — IB PHYSICS SL notes: Use the particle model of matter to link temperature, thermal transfers, the greenhouse effect, gas laws and electric circuits at SL level.Solids — particles are close together in a regular lattice and vibrate abou…
- Thermal equilibrium
- Kelvin scale
- Same temperature
- Internal energy U
- Ideal monatomic gas
- Specific heat capacity
Section 1 of 11States of matter and density
Solids
- Solids particles are close together in a regular lattice and vibrate about fixed positions
Liquids
- Liquids particles are close together but irregular and slide past one another
Gases
- Gases particles are far apart and move randomly at high speed
Density
Density mass ÷ volume, ρ = m ÷ V, in kg m⁻³
Section 2 of 11Temperature and thermal equilibrium
Thermal equilibrium
Thermal equilibrium no net transfer of thermal energy between bodies in contact, because they are at the same temperature
Temperature
- Temperature a statistical property measuring the mean random translational kinetic energy of the particles, Ek = (3/2) kB T
- It only makes sense for a very large number of particles;
- a single particle has kinetic energy but no temperature.
- Bulk motion of a whole object, such as a flying bottle of water, is not counted.
Mixing
- Mixing collisions share energy until the mean kinetic energy per particle is equal, which is the equilibrium temperature
Kelvin scale
- T (K) = θ (°C) + 273 and gas-law and radiation equations need kelvin
Same temperature
- Same temperature gas particles of lower mass have the same mean kinetic energy but a higher typical speed
Section 3 of 11Internal energy, heat capacity and latent heat
Internal energy U
Internal energy U the total random kinetic and potential energy of the particles
Ideal monatomic gas
- U = (3/2) n R T
Specific heat capacity
- Q = m c ΔT, the energy per kilogram per kelvin of temperature changeWhat the symbols mean: E, Q or q = energy transferred (J) · m = mass (kg; g in chemistry calorimetry) · c = specific heat capacity (J kg−1 °C−1; water 4.18 J g−1 °C−1) · ΔT or Δθ = temperature change (°C or K)
- Q is in J, m in kg and c in J kg⁻¹ K⁻¹.
Specific latent heat
- Q = m L, the energy per kilogram to change state at constant temperatureWhat the symbols mean: E or Q = energy to change state without a change of temperature (J) · m = mass (kg) · L = specific latent heat (J kg−1)
- Lf is for solid to liquid and Lv is for liquid to gas.
Heating curve
- Heating curve a plateau is a region of constant temperature during a change of state
Section 4 of 11Thermal energy transfer and black bodies
Conduction
- Conduction transfer by particle collisions and free electrons, mainly in solids
Convection
- Convection transfer by bulk movement of a fluid caused by density differences
Radiation
- Radiation transfer by electromagnetic waves, needing no medium
Black body
Black body a perfect absorber and emitter of radiation
- Luminosity L = σ A T⁴ is the total power emitted.
- Wien's law λmax T = 2.9 × 10⁻³ m K gives the peak wavelength.
Apparent brightness
- Apparent brightness the intensity received, b = L ÷ (4π d²)
Section 5 of 11Greenhouse effect
1Surface emission
- Surface emission the Earth's surface emits infrared radiation
2Absorption
- CO₂, CH₄, H₂O and N₂O molecules have vibrational energy-level differences that match infrared photon energies, so they absorb by resonance
3Re-emission
- Re-emission the radiation is re-emitted in all directions, including back to the surface, so the surface must be warmer to restore the balance
4Enhanced greenhouse effect
- Enhanced greenhouse effect extra warming from human emissions, with concentration measured in ppm
5Not greenhouse gases
- Not greenhouse gases nitrogen and oxygen, because their symmetric diatomic vibrations do not interact with infrared
6Misconceptions
- Misconceptions greenhouse gases absorb infrared, not visible light, and the effect is not ozone depletion, which concerns ultraviolet
Section 6 of 11Amount of substance
Mole
Mole the amount that contains NA = 6.02 × 10²³ particles
Chain
- Chain mass to moles to number of particles, with n = m ÷ M and N = n NA
- The mass of one molecule is M ÷ NA, of order 10⁻²⁶ kg.
Molar volume
- Molar volume at 273 K and 1.01 × 10⁵ Pa one mole of ideal gas occupies about 22.4 dm³
Significant figures
- Significant figures keep the same number as the data
Section 7 of 11Gas laws and kinetic theory
Pressure
- Pressure particles colliding with the walls of the container produce pressure
Fixed amount of gas
- Boyle's law p ∝ 1/V at constant T, Charles's law V ∝ T at constant p, and the pressure law p ∝ T at constant V
Ideal gas
- Ideal gas pV = nRT = N kB T, with temperature in kelvinWhat the symbols mean: p = pressure (Pa) · V = volume (m3) · n = amount of gas (mol) · R = 8.31 J mol−1 K−1 · T = temperature (K = °C + 273)
- R = NA kB links the per-particle and per-mole quantities.
Energy
- Energy internal energy and mean kinetic energy depend only on T
R.m.s. speed
- R.m.s. speed crms = √(3 kB T ÷ m)
- Doubling T increases crms by a factor of √2.
Absolute zero
- Absolute zero the ideal gas model gives zero translational kinetic energy there
Section 8 of 11Electric current and circuits
1
Electric current
Electric current the rate of flow of charge, I = Δq ÷ Δt
2
Charge conservation
- Charge conservation at a junction the current entering equals the current leaving, and in a series loop the current is the same everywhere
3
Ammeter
- Ammeter connected in series; voltmeter — connected in parallel
4
Charge passed
- Charge passed the area under a current–time graph
- 1 A h = 3600 C.
5
Drift speed
- I = n A v q
- Its size is of order 10⁻⁴ m s⁻¹, so an answer in metres per second signals an error.
6
Related quantities
- Related quantities potential difference, e.m.f., resistance R = ρL ÷ A, resistivity, internal resistance, ohmic conductors and the potential divider
7
Units first
- Units first convert mA to A, minutes to seconds and mm² to m²
Section 9 of 11More from the specification
1
Temperature and average kinetic energy
- Temperature is a direct macroscopic measure of the average kinetic energy of particles within a substance;
- higher thermal energy increases particle vibrations and velocities.
2
Latent heat of fusion and vaporisation
- During a phase change, thermal energy supplied breaks intermolecular bonds without raising temperature;
- specific latent heat of fusion (Lf) applies to melting,
- and latent heat of vaporisation (Lv) applies to boiling (Q = m L).
3
Calorimetric determination of thermal properties
- In calorimetry experiments, conservation of thermal energy allows students to determine unknown specific heat capacities (m c delta_T_lost = m c delta_T_gained).
- (such as immersing heated copper metal into water)
4
Thermal conductivity in solids
- Thermal conductivity describes the rate of heat conduction through a material per unit temperature gradient,
- where metals like copper exhibit high conductivity due to free conduction electrons.
5
Copper
- Metal widely used for electrical wires.
6
Fusion
- Joining of light nuclei into a heavier one.
7
Phase change
- Change of matter from one state to another
8
Thermal conductivity
- Material constant relating the rate of conduction to the temperature gradient and area
Section 10 of 11Key terms
| Term | Meaning |
|---|---|
| Thermal equilibrium | No net transfer of thermal energy between bodies at the same temperature. |
| Internal energy | Total random kinetic and potential energy of the particles. |
| Specific latent heat | Energy per kilogram to change state at constant temperature. |
| Mole | The amount of substance containing 6.02 × 10²³ particles. |
| Greenhouse gas | A gas that absorbs infrared radiation emitted by the Earth. |
| Resonance | Large energy transfer when driven at a natural frequency. |
| Electric current | The rate of flow of charge. |
| R.m.s. speed | The square root of the mean squared speed of the particles. |
Section 11 of 11Exam technique
1
Applying a temperature to a single particle — temperature belongs to a large collection of particles.
2
Counting the bulk motion of an object as thermal energy — only the random motion counts.
3
Using °C in gas-law and radiation equations — use kelvin.
4
Thinking nitrogen and oxygen are greenhouse gases — their vibrations do not absorb infrared.
5
Mixing mA with A or mm² with m² — convert units first.
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