Describe why a gas at constant temperature will have a lower pressure if its volume is increased by a factor of three.

Increasing the volume spreads the gas particles over a larger area, reducing the number of collisions per unit time with the walls. Consequently, the pressure falls to one-third of its original value, because pressure is inversely proportional to volume at constant temperature.

Particle lens: Describe arrangement, motion, spacing, collisions, or energy changes only when they are relevant here. This question asks: Describe why a gas at constant temperature will have a lower pressure if its volume is increased by a factor of three. The correct response is Increasing the volume spreads the gas particles over a larger area, reducing the number of collisions per unit time with the walls. Consequently, the pressure falls to one-third of its original value, because pressure is inversely proportional to volume at constant temperature., because density links mass and volume, so the answer must preserve which quantity is being calculated. In Pressure in gases (physics only), the marking point should connect directly to (Physics only) Calculate pressure when volume changes at constant temperature. If the question includes values, the working must keep the appropriate unit and operation; if it is an explanation, it must name the relevant particle behaviour or energy change. This item belongs to Particle model and pressure, so avoid answers that switch to a different quantity, confuse heat with temperature, or describe gas pressure without collisions when collisions are the reason. Checkpoint 552 is distinct because it uses this exact question context and the particle lens rather than a generic particle-model sentence.