Free Boyle's Law MCQs with Answers

1. Boyle's law states that at constant temperature, the volume of a fixed mass of gas is

• A. directly proportional to its pressure
• B. inversely proportional to its pressure
• C. independent of its pressure
• D. proportional to the square of its pressure

Explanation: Boyle's law gives PV equal to a constant, so doubling the pressure halves the volume. A graph of P against V is a hyperbola, while a graph of P against 1 over V is a straight line through the origin, and that straight line is the usual way the law is confirmed experimentally. Volume rising with pressure would describe no real gas.

2. A gas occupies 500 cm3 at 2 atm. At constant temperature, what volume will it occupy at 5 atm?

• A. 200 cm3
• B. 250 cm3
• C. 1250 cm3
• D. 100 cm3

Explanation: Applying P1V1 equal to P2V2 gives V2 equal to 2 times 500 divided by 5, which is 200 cm3. The pressure rose by a factor of 2.5, so the volume must fall by the same factor, and 500 divided by 2.5 is 200. Getting 1250 means the ratio was applied the wrong way round.

3. At constant temperature, doubling the pressure on a fixed mass of gas will

• A. double its volume
• B. halve its volume
• C. leave the volume unchanged
• D. quadruple its volume

Explanation: Boyle's law states that pressure and volume are inversely proportional at constant temperature, so the product PV stays constant and doubling one halves the other. A graph of P against V is a hyperbola, while P against one over V is a straight line. This is why a syringe becomes hard to compress further as the volume shrinks.

4. A gas occupies 500 cm3 at 2 atm. At constant temperature, what volume will it occupy at 1 atm?

• A. 250 cm3
• B. 500 cm3
• C. 1000 cm3
• D. 1500 cm3

Explanation: Using P1V1 equals P2V2, the new volume is 2 multiplied by 500 divided by 1, which is 1000 cm3. Halving the pressure doubles the volume, so an answer smaller than the original must be wrong at a glance. Checking the direction of the change before calculating catches most errors.