If a fixed amount of gas in a balloon is kept at fixed pressure, how does volume change as temperature increases?

• A. Volume is independent of temperature.
• B. Volume decreases as temperature increases.
• C. Volume increases proportionally with temperature.
• D. Volume increases with temperature only if pressure changes.

Answer: (C)

At fixed pressure and with a fixed amount of gas, the volume responds to temperature changes by expanding as temperature rises. This happens because increasing temperature gives the gas molecules more kinetic energy, causing them to collide with the balloon walls more vigorously and push outward. The relationship PV = nRT shows that, when n and P are constant, the volume V is proportional to temperature T (in Kelvin): V ∝ T. So doubling the temperature in Kelvin doubles the volume. Remember to use Kelvin for this proportionality; using Celsius changes the zero point but keeps the linear relationship. In short, the volume increases proportionally with temperature.