Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

Theme B — The Particulate Nature of Matter

B.1.5 Internal Energy — IB Physics HL Revision Notes & Topical Questions

5 min read 9 parts Lesson 7 of 53 1 quiz

📚 IB Physics HL Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
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.
0%read
Lesson summary

B.1.5 Internal Energy — IB PHYSICS SL notes: Define internal energy as the total random kinetic and intermolecular potential energy and explain how it changes with temperature and state.Internal energy = the sum of the total random kinetic energy and the total intermolecular pote…

  • Not included
  • Hidden energy
  • Gaining thermal energy
  • Kinetic part
  • Potential part
  • State changes

Part 1 of 7Definition

Internal energy
Internal energy the sum of the total random kinetic energy and the total intermolecular potential energy of the particles in a substance.
  • U = Ek(random) + Ep(intermolecular), in joules.
Not included
  • Not included the kinetic energy of the whole object moving and its gravitational energy as a whole.
Hidden energy
  • Hidden energy it is stored in the microscopic motion and arrangement of the particles.
Gaining thermal energy
  • Gaining thermal energy the internal energy of a substance increases, and losing it decreases the internal energy.

Part 2 of 7Kinetic and potential contributions

Kinetic and potential contributions
Kinetic part
  • Kinetic part it depends on temperature; raising the temperature raises the mean random kinetic energy.
Potential part
  • Potential part it depends on the separations and forces between particles.
  • It increases when the particles are pulled apart against the attractive forces, as in melting and boiling.
  • It also rises slightly when a substance expands on heating.
Temperature
  • Temperature only a change in the average kinetic energy changes the temperature.
State changes
  • State changes only the potential energy changes, so the temperature stays constant while the internal energy rises.

Part 3 of 7Internal energy of an ideal gas

Internal energy of an ideal gas
No potential part
  • No potential part an ideal gas has no intermolecular forces, so its internal energy is all random kinetic energy.
Monatomic gas
  • U = (3/2)NkBT = (3/2)nRT, where N is the number of particles.
Depends on T only
  • Depends on T only at constant temperature U is constant whatever the pressure or volume.
Use
  • Use this result appears in the first law of thermodynamics.

Part 4 of 7Changing the internal energy

Heating
  • Heating energy is transferred because of a temperature difference.
  • It raises the temperature (Q = mcΔT) or causes a change of state (Q = mL).
    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)
Work
  • Work work done on or by the system also changes U.
  • Rubbing hands together or pumping a bicycle tyre warms them without a temperature difference supplying the energy.
Heat and internal energy
  • Heat and internal energy heat is the energy transferred, while internal energy is the energy stored.
  • An object does not contain heat; it contains internal energy.

Part 5 of 7Comparing systems

Comparing systems
Same temperature, different U
  • Same temperature, different U a kettle of water at 90 °C has more internal energy than a cup at 90 °C, because there are more particles.
Steam and water
  • Steam and water steam at 100 °C has more internal energy than water at 100 °C of the same mass, because the particles are further apart.
Melting ice
  • Melting ice it takes in heat, its temperature stays constant and its internal energy increases.

Part 6 of 7Temperature, heat and internal energy

QuantityMeaningDepends on
TemperatureMean random kinetic energy per particle; sets the direction of energy flowKinetic energy only
Internal energyTotal energy stored in random motion and interparticle potential energyAmount of substance, temperature and state
HeatEnergy transferred because of a temperature differenceProcess, not stored
Analysis
  • Analysis ask whether the mean kinetic energy changed (temperature) and whether the spacing changed.
    • (potential energy)
Ideal gas
  • Ideal gas only the first can occur.

Part 7 of 7More from the specification

1
Microscopic thermal energy in solids
  • Microscopic thermal energy in solids vibrational kinetic energy of lattice atoms defines the internal thermal energy of crystalline solids across Earth.
2
Internal energy
  • Internal energy total random kinetic and potential energy of the particles in a system
3
Specific heat capacity
  • Specific heat capacity energy to raise the temperature of one kilogram by one kelvin, as measured for a copper block
4
Latent heat
  • Latent heat energy for a change of phase at constant temperature, including latent heat of vaporisation and fusion
5
Thermal transfer
  • Thermal transfer conduction, convection and radiation move energy from the surface of a hot object to cooler surroundings
6
Surface temperature
  • Effective temperature of the star's radiating surface.
7
Wavelength
  • Distance between a point on one wave and the same point on the next wave
8
Solid
  • State with a fixed shape and a fixed volume.
9
Fusion
  • Joining of light nuclei into a heavier one.
10
Intensity
  • Power per unit area perpendicular to the wave direction.
11
Apparent brightness
  • The power received per unit area at the observer
12
Thermal equilibrium
  • Constant temperature because energy is absorbed and lost at equal rates
13
Phase change
  • Change of matter from one state to another
14
Thermal conductivity
  • Material constant relating the rate of conduction to the temperature gradient and area
15
Radiation
  • Transfer by electromagnetic waves, requiring no medium
16
Liquid
  • State with a fixed volume that takes the shape of its container.
17
Copper
  • Metal widely used for electrical wires.
18
Convection
  • Transfer of thermal energy by the movement of a heated fluid
19
Conduction
  • Transfer of thermal energy by lattice vibrations and free electrons
20
Luminosity
  • The total power of radiation emitted by a star.
21
Density
  • Mass per unit volume.

Key terms

TermMeaning
Internal energySum of the total random kinetic energy and intermolecular potential energy of the particles
Intermolecular potential energyEnergy stored because of the separations and forces between particles
HeatEnergy transferred because of a temperature difference
WorkEnergy transferred by a force moving through a distance
Ideal gasGas with no intermolecular forces, so internal energy is purely kinetic
Monatomic gasGas whose particles are single atoms

Avoid these mistakes

1
Saying a change in internal energy always changes the temperature — it does not during a change of state.
2
Saying an object contains heat — it contains internal energy.
3
Including the motion of the whole object in internal energy — only random microscopic energy counts.
4
Giving an ideal gas potential energy — it has none.
5
Mixing up temperature and internal energy — a bath and a cup at the same temperature differ in U.

Last updated:

—

  • RNA: 5′ → 3′ 3′ → 5′.
  • : AUG UAC .
  • : UAA, UAG, UGA tRNA (Release Factor) .
\n