Our model of an ideal gas describes gases as a collection of small, rigid spheres, in constant, rapid motion. Because the molecules are very small compared to the space they occupy, we say the molecules have negligible volume. This means that molecules are more likely to collide with the container walls than they are to collide with each other.
Nonetheless, intermolecular collisions are possible and do occur. We refer to the distance a molecule can travel without hitting something else as its mean free path.
Which of the following change possibilities would increase the mean free path of molecules in a sample of confined gas, assuming no change in the number of molecules in the system?