Entropy and the Second Law of Thermodynamics
Discover how systems naturally evolve from order to chaos, visualize statistical distributions, and compare molecular disorder across different phases of matter.
About this simulation
- What
- An interactive Chemistry simulation of Entropy and the Second Law of Thermodynamics.
- Who
- Designed for AP, IB, and A‑Level Chemistry students.
- How
- Runs in any modern browser — drag, adjust, and explore in real time.
Updated 2026-05-26
Key Concepts
Disorder & Diffusion
Spontaneous processes in isolated systems always proceed in a direction that increases the overall disorder (entropy) of the system.
Microstates & Probability
Entropy is a measure of the number of possible microscopic arrangements (microstates, $W$) that correspond to a macroscopic state: $S = k_B \ln W$.
Statistical Distribution
As the number of particles increases, the distribution of states follows a normal (Gaussian) curve, with extreme states becoming vanishingly improbable.
Phase & Molecular Motion
Entropy increases from solid to liquid to gas as molecular motion and disorder increase: S(solid) < S(liquid) < S(gas).
The Second Law
The total entropy of an isolated system (the universe) always increases over time in any spontaneous process: ΔS(total) > 0.
Exam specification coverage
Understanding Entropy and the Second Law
Entropy (S) is a fundamental thermodynamic quantity that measures the degree of disorder, randomness, or microstate multiplicity in a system. The Second Law of Thermodynamics asserts that the total entropy of an isolated system can never decrease over time; it can only remain constant or increase.
Under the statistical definition pioneered by Ludwig Boltzmann, entropy is directly related to the number of microstates ($W$) available to a system: $S = k_B \ln W$. When particles spread out, or when thermal energy is distributed, the system accesses macrostates with much higher probabilities simply because there are far more microstates corresponding to these mixed or uniform states.
Use our interactive simulator to explore these statistical and thermodynamic concepts in real time. Observe how hot and cold particles mix, watch statistical distributions emerge from random processes, and compare the molecular disorder of ice, water, and steam at the molecular level.
Frequently Asked Questions
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