Answer
The temperature is the same, and the pressure is halved.
Work Step by Step
This is a process known as an adiabatic free expansion of an ideal gas. There is no pressure/piston for the gas to expand against, so it does zero work. The insulation means that no heat enters or leaves, so the internal energy stays the same. The ideal gas’s temperature therefore doesn’t change.
Using the ideal gas law, PV=nRT, doubling the volume will halve the pressure under constant temperature conditions.
