If the pressure on a confined liquid is doubled while the temperature remains constant, the volume will

• A. Increase
• B. Decrease
• C. Remain the same
• D. Double

Answer: (C)

Liquids are nearly incompressible, so increasing pressure while keeping temperature fixed changes their volume very little. The amount of compression is governed by the bulk modulus: B = -V ΔP / ΔV. Since liquids have a large bulk modulus, a given rise in pressure produces only a tiny decrease in volume. If the pressure is doubled, the resulting change in volume is extremely small, so the volume is effectively the same for practical purposes. The other options would require a noticeable expansion, a noticeable contraction, or a large contraction, which doesn’t occur with a simple doubling of pressure at constant temperature.