Gas particles move randomly in constant motion, with negligible volume and collisions that are perfectly elastic.
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The kinetic molecular theory is a model that explains gas behaviour in terms of particle motion. It assumes gas particles are tiny compared with the distances between them, so their own volume is negligible. The particles move randomly in straight lines and collide elastically with each other and with the container walls, so no kinetic energy is lost in collisions. Pressure arises from the force of these wall collisions, and the average kinetic energy of the particles is proportional to the absolute temperature. The theory explains Boyle's, Charles's and Gay-Lussac's laws and is the foundation of the ideal gas law.
Key ideas: Key postulates: negligible particle volume, no attractions, random elastic collisions, and average kinetic energy equal to (3/2)kT. From these, P = (1/3)(N/V) m v_rms^2 follows, linking microscopic motion to measurable pressure. Use the theory qualitatively to predict how P changes when V, T or N changes: more frequent or harder wall hits mean higher pressure.
Common mistakes and connections: A common error is saying all molecules at a given temperature have the same speed; there is a distribution. Another is believing heavier gases have more kinetic energy at the same T. The postulates fail at high pressure and low temperature, leading to real gas models like van der Waals.
Gas particles are tiny, far apart and in constant random motion; collisions with the walls create pressure. Change temperature and volume to see the effect. The interactive lesson shows this as a live animation or chart.
At the same temperature, hydrogen and oxygen molecules have the same average kinetic energy, but hydrogen molecules move about four times faster because they are much lighter.
Gas particles move randomly in constant motion, with negligible volume and collisions that are perfectly elastic.
Kinetic Molecular Theory is a beginner topic in States of Matter & Solutions. It needs no earlier chemistry lessons and is a good starting point.
Study these earlier topics in States of Matter & Solutions first: States of Matter.
The next topics in States of Matter & Solutions are Plasma and Bose-Einstein Condensate.
Yes. The interactive lesson includes a self-check question on Kinetic Molecular Theory, and the States of Matter & Solutions quiz draws on every topic in this area.
Kinetic Molecular Theory is topic 2 of 109 in States of Matter & Solutions.