IB Physics HL topic guide

The Particulate Nature of Matter

The Particulate Nature of Matter is a core part of IB Physics HL. This guide connects the syllabus ideas behind Specific Heat Capacity, Latent Heat, Heat Transfer Mechanisms, The Greenhouse Effect, Climate Feedbacks and Equilibrium Temperature and 5 more units, shows how they appear in worked problems, and points you to the formulas and full lessons needed for exam revision.

What you will learn

The Particulate Nature of Matter syllabus outline

The units below follow the structure used in the full Study to Learn course. Use the outline to identify exactly which idea needs attention, then work through the public example before continuing to the complete lesson path.

B.1

Specific Heat Capacity

Temperature, Heat and Internal Energy · Specific Heat Capacity — Calculations and Calorimetry · Heat Capacity and Thermal Equilibrium

B.2

Latent Heat

Phase Changes and Latent Heat · Heating Curves and Multi-Stage Problems

B.3

Heat Transfer Mechanisms

Conduction, Convection and Thermal Radiation · Blackbody Radiation — Stefan–Boltzmann and Wien's Laws

B.4

The Greenhouse Effect

The Greenhouse Effect · Modelling the Greenhouse Effect

B.5

Climate Feedbacks and Equilibrium Temperature

Modelling Earth's Equilibrium Temperature · Climate Feedback Loops

B.6

Ideal Gas Laws

Ideal Gas Laws · Units and Absolute Quantities

B.7

Kinetic Theory of Gases

Kinetic Theory · Maxwell-Boltzmann Distribution and Degrees of Freedom

B.8

Thermodynamics

First Law of Thermodynamics · Second Law and Entropy

B.9

DC Circuits

Current, Resistance and EMF · Series and Parallel Circuits · Potential Dividers and Sensors

B.10

Capacitors

Capacitance and Energy Storage · RC Circuits and Charging/Discharging

Free worked preview

First Law of Thermodynamics

This complete preview comes from the Thermodynamics unit. It introduces the core language, shows the method in context, and gives you a real example of the lesson quality before you create an account.

The First Law of Thermodynamics

Where the gas laws described gases in equilibrium, thermodynamics — beginning with $\Delta U = Q + W$ — describes what happens when that equilibrium is disturbed by heating, compression, or expansion. It is the most general statement of energy conservation in physics, and it lets you track energy through isothermal, adiabatic, isobaric, and isovolumetric processes, reading the work done off a p–V diagram.

First LawEnergy is conserved — the internal energy of a system can only change if heat flows in/out or work is done on/by it:

\Delta U = Q + W

where

\Delta U

change in internal energy of the gas (J) — positive means internal energy increased (gas got hotter or bonds formed)

Q

heat added to the system (J) — positive if heat flows IN; negative if heat flows OUT

W

work done ON the system (J) — positive if gas is compressed; negative if gas expands (does work on surroundings)

IB sign convention: W = work done ON system (compression is +W). Some textbooks write ΔU = Q − W where W is work done BY the system — watch the sign carefully.

Work Done by/on a Gas

W_{by} = p\Delta V \quad (\text{constant pressure})

where

W_{by}

work done BY the gas on its surroundings (J) — positive when gas expands (ΔV > 0); note W_on = −W_by

p

pressure of the gas (Pa) — constant for an isobaric process

\Delta V

change in volume of the gas (m³) — positive for expansion

For a non-constant pressure process, work = area under the p–V graph. A cycle on a p–V diagram represents a heat engine; the area enclosed equals the net work output per cycle.

Worked Example — First Law Application 450 J of heat is added to a gas, which simultaneously expands and does 120 J of work on its surroundings. Find the change in internal energy.

Q = +450 J (heat added in), W_by = +120 J, so W_on = −120 J
ΔU = Q + W_on = 450 + (−120) = +330 J
The gas has 330 J more internal energy — it is now hotter.

General: W_by = area under p–V graph.

Thermodynamic Processes

Process	Constant	ΔU	Q	W (on)
Isothermal	T	0	$Q=\text{area under }p\text{–}V\text{ curve}$	$-Q$
Adiabatic	Q = 0	W (on)	0	ΔU
Isobaric	p	$Q+W_{on}=Q-p\Delta V$	—	$-p\Delta V$
Isovolumetric	V	Q	ΔU	0

Note on the isothermal row: pressure is not constant during an isothermal process (p and V vary together so that T stays fixed), so W = pΔV does not apply here — that shortcut is only valid at constant pressure (the isobaric row). For an isothermal process, ΔU = 0, so Q = W_by = the area under the p–V curve for that process.

Reviewed by the Study to Learn editorial team · Updated 2026-07-24