Question

When the volume of a gas is decreased at constant temperature the pressure increases because the molecules

• A. strike unit area of the walls of the container more often
• B. strike the unit area of the walls of the container with higher speed
• C. strike the unit area of the wall of the container with lesser speed
• D. move with more kinetic energy

Answer 1

The correct option is A strike unit area of the walls of the container more often

We first note that the speed and hence the kinetic energy of the molecules of an ideal gas depends solely on temperature and since here temperature remains constant, the pressure cannot increase due to factors mentioned in options B,C and D
Now A is correct and we explain why.
Consider a small area on the wall of the container. Previously when volume was high, it had a lower probability of being hit by a molecule but now space is less, so it will be hit by more molecules so, more pressure will be generated on this area.
Hence pressure increases