2.1.1 System and surroundings System:the specific part of the universe we are studying Surroundings:the rest of the universe outside the system Open system:a system can exchange mass and energy with its surroundings Closed system:a system exchanges energy but not matter with its surroundings Isolated system:a system exchange neither mass nor energy with its surroundings2.1.1 System and surroundings System：the specific part of the universe we are studying Surroundings：the rest of the universe outside the system Open system: a system can exchange mass and energy with its surroundings Closed system: a system exchanges energy but not matter with its surroundings Isolated system: a system exchange neither mass nor energy with its surroundings