Answer:
The portion of the universe that we single out to study is called the SYSTEM
The SURROUNDINGS are everything else
Step-by-step explanation:
The universe is composed of system and surrounding.
The system is the portion of the universe that is under the observation. It consists of molecules that are undergoing a chemical reaction.
Whereas, the surrounding or environment is the portion of the remaining universe that is not under observation, but can interact with the system.
For example: A cylinder containing hydrogen and oxygen gas.
In this example, the molecules inside the cylinder is the system. Whereas, the cylinder, piston and the surrounding space is the surrounding.