What is the relationship between pressure and volume for a fixed mass of gas at constant temperature?

The pressure multiplied by the volume of a fixed mass of gas is constant at constant temperature. This means that if the volume decreases, the pressure increases, and vice versa.

Method lens: First identify the measured quantity, then match the equation or particle idea to the command word. This question asks: What is the relationship between pressure and volume for a fixed mass of gas at constant temperature. The correct response is The pressure multiplied by the volume of a fixed mass of gas is constant at constant temperature. This means that if the volume decreases, the pressure increases, and vice versa., 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 536 is distinct because it uses this exact question context and the method lens rather than a generic particle-model sentence.