According to Charles' law, what happens to the volume of a gas when temperature increases at constant pressure?

• A. The volume increases.
• B. The pressure increases.
• C. The volume decreases.
• D. The temperature decreases.

Answer: (A)

Charles’ law shows that at constant pressure, a gas’s volume changes directly with its absolute temperature. As temperature rises, the gas molecules move faster and exert more energy on the container walls. To keep pressure the same, the container must expand, so the volume increases. Using the Kelvin scale is important because direct proportionality holds with absolute temperature, not with Celsius. If temperature doubles in Kelvin while pressure stays constant, the volume tends to double as well. So, when temperature increases at constant pressure, the volume increases.