Final answer:
The branch of chemistry that studies what happens when matter undergoes change is Physical chemistry. It uses principles of physics and chemistry to understand the physical properties of molecules, and how they interact and react.
Step-by-step explanation:
The area of chemistry that focuses on studying what happens when matter undergoes change is known as Physical chemistry. Physical chemistry integrates the principles of physics and chemistry to understand the physical properties of molecules, the forces that act upon them, and how they interact and react with each other. This branch of chemistry is primarily concerned with energy changes and observable phenomena that occur during chemical reactions.
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