Why do real gases not behave exactly like ideal gases?

Real gases are always hotter than ideal gases.

Real gas particles have significant volume.

Real gas particles have perfectly elastic collisions.

Real gas particles are smaller than ideal gas particles.

Real gas particles have more complex interactions than ideal gas particles.

There are more than one answer!

Real gas particles have significant volume

Real gas particles have more complex interactions than ideal gas particles

The answer is;

Real gas particles have significant volume Real gas particles have more complex interactions than ideal gas particles

When using the ideal gas equation (PV = nRT) particular assumptions are made. That the molecules of the gas occupy negligible space and that the molecules only interact through elastic collision. However, the molecules of real gas have a finite volume and they interact also through intermolecular forces (such as in partially-charged molecules).