A gas confined in a rigid, perfectly insulated container is suddenly allowed to expand into an evacuated chamber inside the container (free expansion). Which combination of signs for Q, W, and ΔU best describes the gas during this expansion?
a) Q<0,W=0,ΔU<0
b) Q=0,W=0,ΔU=0
c) Q=0,W<0,ΔU>0
d) Q=0,W>0,ΔU<0