system has no mass transfer, but allows
energy transfer across the system boundary. Closed
are also called non-flow systems, control-mass systems or
A solid is a closed system (no mass transfer across boundary)
Expanding or compressing a gas can also be a closed system if there is no flow or major leakages.
Energy Equation (1st Law of Thermodynamics);
U2-U1 = Q - W Where U = internal energy
(J) Q = heat transfer (J) (+ = heat IN) W = work transfer
(J) (+ = work OUT)
WARNING! The (Kinsky) book uses this
definition U2-U1 = Q - W. (i.e. Positive work is work done BY the system (not To the system
which is more consistent with the concept of a Free Body Diagram)
See Ref 1
Confused? Just remember... Expansion = Positive Work !
important equation (1st Law of Thermodynamics) is written both
ways in different books -
Physics books are the same as our text (Kinsky), Chemistry books us
defnition. Essentially all modern textbooks
of physical chemistry use U=Q+W, such as those
by Peter Atkins and Ira Levine,
but all textbooks on physics (including Kinksy) define work as U=Q-W, the work done
system - which is surprisingly contrary to the concept of the Free Body
Diagram (Where signs are determined by what is done "TO THE BODY"). I
prefer the Chemistry way, but we will stick to the textbook to avoid confusion.