If a gas at constant pressure has V1 = 1.0 L at T1 = 300 K and is heated to T2 = 420 K, what is V2?

If a gas at constant pressure has V1 = 1.0 L at T1 = 300 K and is heated to T2 = 420 K, what is V2?

• A. 1.4 L
• B. 1.0 L
• C. 1.2 L
• D. 1.6 L

Answer: (A)

When pressure is kept constant, a gas’s volume changes in direct proportion to its temperature (in Kelvin). This is Charles’s law: V ∝ T at constant P. So V2 = V1 × (T2/T1). Using T1 = 300 K and T2 = 420 K, V2 = 1.0 L × (420/300) = 1.4 L. The 1.4 L result reflects the 40% increase in temperature from 300 K to 420 K. If the temperature only reached 360 K, the volume would be 1.2 L; if it reached 480 K, the volume would be 1.6 L. But with 420 K, 1.4 L is the correct volume.

When pressure is kept constant, a gas’s volume changes in direct proportion to its temperature (in Kelvin). This is Charles’s law: V ∝ T at constant P. So V2 = V1 × (T2/T1). Using T1 = 300 K and T2 = 420 K, V2 = 1.0 L × (420/300) = 1.4 L.

The 1.4 L result reflects the 40% increase in temperature from 300 K to 420 K. If the temperature only reached 360 K, the volume would be 1.2 L; if it reached 480 K, the volume would be 1.6 L. But with 420 K, 1.4 L is the correct volume.