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Kinetic Molecular Theory

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Kinetic molecular theory (KMT) is the particle-level story behind gas behavior: particles in constant random motion, with negligible volume, no attractions, and elastic collisions. Their average kinetic energy is proportional to the Kelvin temperature. The Maxwell-Boltzmann distribution displays the range of particle speeds at a given temperature.

UNIT 3 TOPIC 3.5 • KINETIC MOLECULAR THEORY KINETIC MOTION MAP A model of ideal gases: five postulates that explain how particles behave. 1 CONSTANT RANDOM MOTION Gas particles move in constant, random, straight-line motion. 2 ELASTIC COLLISIONS Collisions with particles and walls are elastic — no net kinetic energy is lost. 3 NEGLIGIBLE PARTICLE VOLUME Particle volume is negligible vs. the volume of the container. 4 NEGLIGIBLE IMF ATTRACTIONS no net force Negligible attractive or repulsive forces (IMFs) act between particles. SPEEDS VARY: MAXWELL–BOLTZMANN DISTRIBUTION Number of particles Molecular speed Lower T (T₁) Higher T (T₂) T₂ > T₁ 5 AVERAGE KE ∝ TEMPERATURE Average kinetic energy depends ONLY on absolute temperature (K). At the same T, ALL gases have the same average kinetic energy. Higher T → greater average KE (distribution shifts right, broadens). CED ANCHOR SPQ-4 · Kinetic Molecular Theory KMT models an ideal gas: tiny particles in constant random straight-line motion, elastic collisions, negligible volume and negligible IMFs. Average kinetic energy is proportional to absolute temperature (K) — same for all gases at the same T. AP Chemistry · Unit 3 · Properties of Substances & Mixtures
Kinetic molecular theory pictures a gas as tiny particles in constant, random, straight-line motion with elastic collisions. Temperature (in Kelvin) sets the average kinetic energy; the Maxwell-Boltzmann distribution shows the spread of speeds, which broadens and shifts right as temperature rises.
Maxwell-Boltzmann Lab · Open the sandbox →

The misreads cluster around temperature and the particle model: forgetting that it is the Kelvin temperature that sets kinetic energy, and misinterpreting what the speed distribution shows as temperature changes. KMT is the reasoning that connects a microscopic picture to the ideal gas law.

The work

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Lesson
Kinetic Molecular Theory ›

KMT explains gas behavior from particle motion, with kinetic energy tied to Kelvin temperature and speeds spread by the Maxwell-Boltzmann distribution. The lesson reads the distribution and closes with a ten-scenario check.

Skill check · 10 scenarios
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Diagnostic
10-item topic check ›

Ten items on kinetic molecular theory: the particle model of a gas, kinetic energy set by Kelvin temperature, and reading the Maxwell-Boltzmann speed distribution.

Not started · 10 items · ~15 min
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Targeted Practice
Drill a single misconception ›

Pick one of the failure modes you missed and drill it on its own. The round is adaptive: two correct in a row clears the misconception and moves you to the next.

Take the diagnostic to identify your misconceptions
Diagnostic first