Physical chemistry is a domain in physical science which overlaps with chemical science.
Many branches of thought and ideas that were developed by physicists over the centuries have been applied to chemistry and that created new branches of knowledge. Actually there was no difference that this something is chemistry or physics as the knowledge developed; it's just as somebody needing a type of a knowledge and investigating it and finding out something new for example when we tried to understand the way heat is transfered and how much work we can extract from it; it gave rise to the branch of knowledge called thermodynamics and some time later somebody realized that the thermodynamics is universal phenomenon and that it can be applied to chemical systems. So when physics students are taught merely thermodynamics chemistry students are taught chemical thermodynamics which comes under physical chemistry.
The study of rates of reactions also come under physical chemistry and is called chemical kinetics as opposed to kinetics in physics which is about the motion of objects.But the big boost to physical chemistry came in the 20th century when the scope of study went inside the atom and we needed to explain the things that are happening on that scale; now physicist would contest that this is not the realm of chemistry but that of physics. Well in reality this is a field which both the sciences share. As the atomic theory evolved with the introduction of quantum mechanics - which is the single most influential scientific branch of the 20th century.