Systems and Surroundings: The First Law of

Thermodynamics

The term system is used to describe the particular part of the universe we are focusing our attention
on: a beaker, a cell, Earth and its atmosphere, et cetera; everything outside the system is considered
the surroundings or environment (i.e., system + surroundings = universe). A system may be classified
as:

BASIC CONCEPT

Three   Types   of  Systems

You may have learned that energy, though interconvertible among all its different forms (kinetic,
potential, et cetera), is conserved: The total amount of energy has to be constant. This is true of a
particular system only if it is isolated. Since energy can neither go in nor go out, it has to be
conserved. If the system is closed or open, the amount of energy in the system can certainly change.
A system can exchange energy with its surroundings in two general ways: as heat or as work. The

Isolated—when   it  cannot  exchange    energy  or  matter  with    the surroundings,   as  with    an

insulated   bomb    reactor or  a   well-insulated  Thermos flask

Closed—when it  can exchange    energy  but not matter  with    the surroundings,   as  with    a   steam

radiator    or  a   stoppered   test    tube    out of  (and    into)   which   heat    can flow

Open—when   it  can exchange    both    matter  and energy  with    the surroundings,   as  with    a   pot of

boiling water:  Water   molecules   are escaping    into    the gas phase,  bringing    energy  with    them.

Isolated

Closed

Open