Which statement correctly describes Charles' Law?

• A. At constant volume, pressure is directly related to temperature.
• B. At constant temperature, the volume and pressure of a gas are inversely related.
• C. At constant pressure, volume is directly related to temperature.
• D. At constant temperature, the volume remains constant regardless of pressure.

Answer: (C)

Charles' Law states that when pressure is kept constant, the volume of a gas increases directly as its temperature. That’s why the correct statement says that at constant pressure, volume is directly related to temperature. Remember, temperature must be in Kelvin for this direct proportionality to hold, since the relationship relies on reaching absolute zero. If you double the temperature in Kelvin, the volume doubles, assuming amount of gas and pressure stay the same. The other ideas mix up which variable is held constant: keeping volume constant relates pressure to temperature, and keeping temperature constant relates pressure and volume inversely; thus they don’t describe Charles' Law.