why is a gas easier to compress than liquid or a solid?

Question

the space between gas particles is ,uch less than the space between liquid or soild particles.

its volume in creases more under pressure than an equal volume of liquid does.

Answer 1

Because there is more space between the molecules in a gas - not less. i.e. it is less dense. There is an upper limit to which a substance can be compressed before atomic forces take over because the particles are too close together and cannot be pushed any closer together [compressed any further].

Answer 2

There is a lot more space in between molecules of a gas than between molecules of a liquid (in 'contact') and of a solid (in contact + crystal structure).

In addition to the repulsion between electron clouds that keep molecules apart in any form of matter, gasses also have the fact that hot molecules are bouncing off each other at a fantastic rate, keeping each other even further apart and breaking any polarisation (or crystaline) bond that may try to form.

When the temperature in a gas drops, the energy available for the bouncing-off-each-other diminishes and, at some point, it is no longer sufficient to prevent the bonds that create the liquid (or solid) form.

Same thing applies with increasing pressure: If you raise the pressure high enough, you may be able to put molecules in contact, forming a liquid (or even solid) despite the high temperature. However, in most substances, there is a temperature above which the polariation bond cannot form (therefore, no liquid) even if the pressure keeps the molecules in very close contact.

As for the volume of a gas increasing with temperature: as the bouncing-off-each-other energy increases, each molecules pushes the other molecules away with more and more force, as they bounce off them with more and more speed.

In a liquid or a solid, the weak bonds (compared to the chemical bond, that is) do retain the molecules closer to each other, even though there is still some (weak) bouncing-off-each-other activity going on.