Final answer:
The coefficient of volume expansion is a material constant that describes its volume change with temperature and is independent of pressure because it assumes infinitesimal pressure changes. Volume is directly proportional to temperature at constant pressure, while at constant temperature, volume is inversely proportional to pressure.
Step-by-step explanation:
The coefficient of volume expansion is independent of pressure and can be considered a constant for a given material. This coefficient describes how much a material's volume changes with temperature. The reason it is independent of pressure is that it is defined for an infinitesimal change in volume with temperature, under the condition that the pressure change is so small that it does not affect the volume significantly.
Volume is directly proportional to temperature when the pressure is constant, according to one of the gas laws known as Charles's Law. This is because, at constant pressure, increasing the temperature will give the particles in the material more energy, causing them to move apart and occupy more space, hence increasing the volume.
On the other hand, when temperature is constant, according to Boyle's Law, the volume of a fixed amount of gas is inversely proportional to its pressure. If you increase the pressure, the volume will decrease, provided the temperature does not change.