1. Increased Density: The gas molecules are forced closer together, leading to a higher density.

2. Increased Pressure: The molecules collide more frequently with the walls of the container, resulting in a higher pressure. This is the fundamental principle behind the operation of compressors.

3. Reduced Volume: The space occupied by the gas decreases as the molecules are squeezed closer together.

4. Temperature Change: The compression process can lead to an increase in temperature. This is because the work done in compressing the gas is converted into internal energy, which manifests as increased molecular motion and therefore higher temperature.

5. Potential for Phase Change: If the compression is significant enough, the gas may transition into a liquid state. This is because the increased pressure and density can overcome the intermolecular forces that keep the molecules apart in a gaseous state.

Example: Imagine a bicycle pump. When you push down on the handle, you're compressing the air inside the pump. You can feel the pressure increase, and the air inside gets hotter (you may even notice a bit of condensation forming on the outside of the pump).

Important Note: The exact changes in density, pressure, and temperature depend on the specific gas being compressed and the conditions of the compression. These are governed by the ideal gas law and other thermodynamic principles.