Which statement about the relationship between pressure and temperature for gases is true?

• A. Directly related
• B. Inversely related
• C. Not related
• D. They are always equal

Answer: (A)

When a gas is confined at a fixed volume, its pressure rises as the temperature increases. This happens because higher temperature means the gas molecules move faster, so they collide with the container walls more often and with greater force. Those more frequent, stronger collisions push the walls harder, increasing pressure. Because of this, pressure is directly proportional to the absolute temperature (P ∝ T, using Kelvin). If the temperature were to double (in Kelvin) while the volume stays the same, the pressure would roughly double as well. This is why a sealed container heats up and the pressure climbs in the sun, or why a balloon left in a hot car expands.

So the accurate statement is that pressure and temperature are directly related under constant volume. The other options don’t fit because pressure does not remain unchanged with temperature, and they aren’t always equal since pressure and temperature are proportional, not necessarily equal.