A321 pilot reported encountering wake turbulence on approach to ORD in trail of a heavy jet.

Narrative

While on the ILS at ORD; we were assigned 180 knots while following a heavy aircraft flying approximately 170 knots. As we closed the gap; we encountered wake turbulence and experienced about 20° of uncommanded roll. We reduced speed to reestablish spacing and exited the wake. The approach and landing were completed uneventfully. After landing; we advised ATC of the wake encounter and speed compression.Cause: The event was influenced by compressed spacing behind a heavy aircraft due to the assigned 180-knot approach speed while the heavy was flying closer to 170 knots; which increased our closure rate and placed us in their wake. Heavy arrival traffic into O'Hare reduced sequencing flexibility; and radio congestion delayed our ability to communicate adjustments with ATC during a critical phase of flight. These factors collectively led to reduced spacing and the resulting wake turbulence encounter.