Theme B — The Particulate Nature of Matter
B.1.6 Thermal Equilibrium — IB Physics HL Revision Notes & Topical Questions
5 min read 9 parts Lesson 8 of 53 1 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
B.1.6 Thermal Equilibrium — IB PHYSICS SL notes: Explain thermal equilibrium, the direction of energy transfer and the zeroth law, and predict the final temperature of objects in contact.Direction — thermal energy is always transferred from a hotter region to a cooler region.Micr…
- Microscopic view
- Thermal contact
- Ice in water
- Thermometers
- Meaning of temperature
- Isolated system
Part 1 of 7Energy flow and temperature
1Direction
- Direction thermal energy is always transferred from a hotter region to a cooler region.
2Microscopic view
- Microscopic view faster particles of the hot object pass kinetic energy to slower particles of the cold object by collisions at the boundary.
3Thermal contact
- Thermal contact the two regions must be in thermal contact for energy to flow.
4Result
- Result the hot object cools and the cold object warms until their temperatures are equal.
Part 2 of 7Thermal equilibrium
Thermal equilibrium
Thermal equilibrium
Thermal equilibrium two substances in contact no longer exchange net thermal energy, because they are at the same temperature.
Particles
- Particles individual particles still exchange energy, but equal amounts go in both directions.
Final temperature
- Final temperature it depends on the initial temperature difference and on the masses and specific heat capacities.
Ice in water
- Ice in water the ice warms as the water cools until they reach one temperature.
Part 3 of 7The zeroth law
Zeroth law
- Zeroth law if A is in thermal equilibrium with B, and B with C, then A is in thermal equilibrium with C.
Thermometers
- Thermometers a thermometer B gives the same reading for A and C if A and C are at the same temperature.
Meaning of temperature
- Meaning of temperature it is a property that is equal for all systems in mutual equilibrium.
Part 4 of 7Final temperature of a mixture
Final temperature of a mixture
Isolated system
- Isolated system energy lost by the hotter body equals the energy gained by the colder one.
Equation
- Equation m1c1(T1 − Tf) = m2c2(Tf − T2).
- T1 and T2 are the initial temperatures of the hot and cold bodies and Tf is the common final temperature.
Solution
- Tf = (m1c1T1 + m2c2T2)/(m1c1 + m2c2), a weighted average.
Check
- Tf lies between T1 and T2, nearer to the body with the larger mc.
Units
- Units temperature differences can be in °C or K.
Layout
- Layout write the energy lost, the energy gained and the equation setting them equal.
State changes
- State changes check whether there is enough energy to complete the change before assuming a final temperature.
Part 5 of 7Equilibrium with the surroundings
1Cooling to room temperature
- Cooling to room temperature a hot cup cools fastest at first, when the temperature difference is greatest.
2Cooling curve
- Cooling curve temperature against time has a decreasing gradient and approaches room temperature asymptotically.
3Rate of cooling
- Rate of cooling the gradient of the tangent; multiply by mc for the power lost.
4Steady state is not equilibrium
- Steady state is not equilibrium a rod with one end in a flame and the other in ice has constant temperatures but continuous energy flow.
Part 6 of 7Practical issues
Calorimetry
- Calorimetry energy is lost to the container and the air, and the calorimeter absorbs energy.
Improving accuracy
- Improving accuracy insulate, stir, use a lid and include the heat capacity of the container.
Effect of loss
- Effect of loss the measured rise is smaller, so the specific heat capacity of the sample comes out too large.
Part 7 of 7More from the specification
1
Zeroth law of thermal equilibrium
- Zeroth law of thermal equilibrium thermal energy transfers cease when bodies achieve identical temperature, governing terrestrial equilibrium across Earth.
2
Thermal conduction mechanism
- Thermal conduction mechanism energetic vibrating particles in hot solids collide with neighbouring atoms and free electrons to transfer kinetic energy.
3
Convection in fluids
- Convection in fluids warm fluid regions expand and decrease in density, rising to create continuous circulating convection currents.
4
Latent heat of vaporisation
- Latent heat of vaporisation energy required to separate liquid molecules against intermolecular attractions into gas at boiling temperature.
5
Thermal Equilibrium and Temperature
- Two thermodynamic systems are in thermal equilibrium when no net thermal energy flows between them, indicating that both systems share the same temperature (Zeroth Law).
6
Mechanisms of Heat Transfer
- Thermal energy transfers via conduction through particle collisions in solids, convection via bulk buoyant movement in liquids and gases,
- and electromagnetic thermal radiation in a vacuum.
7
Specific Heat Capacity and Calorimetry
- Specific heat capacity c is the energy required to raise the temperature of 1 kg of a substance by 1 K (Q = mcΔT); in mixtures of copper and water, heat lost equals heat gained.What 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)
8
Latent Heat of Phase Changes
- Latent heat of fusion and vaporisation quantify the thermal energy absorbed or released during phase transitions at constant temperature (Q = mL) without changing particle kinetic energy.What 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)
9
Surface temperature
- Effective temperature of the star's radiating surface.
10
Wavelength
- Distance between a point on one wave and the same point on the next wave
11
Solid
- State with a fixed shape and a fixed volume.
12
Fusion
- Joining of light nuclei into a heavier one.
13
Intensity
- Power per unit area perpendicular to the wave direction.
14
Apparent brightness
- The power received per unit area at the observer
15
Phase change
- Change of matter from one state to another
16
Thermal conductivity
- Material constant relating the rate of conduction to the temperature gradient and area
17
Internal energy
- Total kinetic and potential energy of the particles in a system
18
Radiation
- Transfer by electromagnetic waves, requiring no medium
19
Liquid
- State with a fixed volume that takes the shape of its container.
20
Copper
- Metal widely used for electrical wires.
21
Convection
- Transfer of thermal energy by the movement of a heated fluid
22
Conduction
- Transfer of thermal energy by lattice vibrations and free electrons
23
Molecule
- Tiny particle of the fluid, too small to be seen.
24
Luminosity
- The total power of radiation emitted by a star.
25
Density
- Mass per unit volume.
Key terms
| Term | Meaning |
|---|---|
| Thermal equilibrium | State with no net transfer of thermal energy between bodies in contact |
| Thermal contact | Arrangement allowing thermal energy to pass between objects |
| Zeroth law | If A and B and B and C are each in equilibrium, then A and C are in equilibrium |
| Heat capacity | Energy needed to raise the temperature of an object by 1 K, C = mc |
| Calorimeter | Insulated container used to measure thermal energy changes |
| Steady state | Condition in which temperatures are constant but energy still flows |
Avoid these mistakes
1
Thinking thermal energy flows from the object with more energy — it flows from higher temperature.
2
Believing nothing happens at equilibrium — particles still exchange energy equally in both directions.
3
Giving a final temperature outside the range of the two initial values — it lies between them.
4
Ignoring the container in calorimetry — it absorbs energy too.
5
Treating a steady state as equilibrium — energy still flows continuously.
Marked practiceQuizzes for this lesson
Last updated:
3 & IGCSE —
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- : Kc .