Explain why decreasing the volume of a gas at constant temperature increases its pressure.

Decreasing the volume of a gas at constant temperature increases its pressure because the gas particles have less space to move. This leads to more frequent collisions with the walls of the container, resulting in a higher force exerted on the walls, which increases the pressure.

Comparison lens: State both sides of the comparison so the contrast is explicit rather than implied. This question asks: Explain why decreasing the volume of a gas at constant temperature increases its pressure. The correct response is Decreasing the volume of a gas at constant temperature increases its pressure because the gas particles have less space to move. This leads to more frequent collisions with the walls of the container, resulting in a higher force exerted on the walls, which increases the pressure., 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) State that pressure multiplied by volume is constant for a fixed mass of gas 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 533 is distinct because it uses this exact question context and the comparison lens rather than a generic particle-model sentence.