Question detail
What happens to gas pressure when the volume of a fixed mass of gas is decreased at constant temperature (Particle motion in gases)
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Particle model and pressure
Question
- A. The pressure decreases.
- B. The pressure increases.
- C. The temperature decreases.
- D. The gas expands.
Answer
The correct answer is The pressure increases..
Explanation
Cause lens: Name the cause, then state the effect on particles, pressure, density, or energy. This question asks: What happens to gas pressure when the volume of a fixed mass of gas is decreased at constant temperature (Particle motion in gases). The correct response is The pressure increases., because gas pressure comes from particle collisions with container walls. In Particle motion in gases, the marking point should connect directly to distinguish gas pressure from atmospheric pressure in particle-model explanations. 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 508 is distinct because it uses this exact question context and the cause lens rather than a generic particle-model sentence.
Common mistake
Confusing gas pressure with atmospheric pressure
Students often say that gas pressure is the same as atmospheric pressure, or that the two pressures are interchangeable in particle‑model explanations.
Explain that gas pressure is the force per unit area exerted by gas particles on the walls of their own container, while atmospheric pressure is the force per unit area exerted by the air outside the container. In particle‑model terms, gas pressure arises from collisions of the gas’s own particles, whereas atmospheric pressure results from collisions of the surrounding air particles. Clarify that the two pressures can have the same numerical value (e.g. 1 bar) but they are distinct physical quantities and should be treated separately in explanations.
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