Lecture 2 Flashcards
First law of thermodynamics
energy can neither be created or destroyed
change in energy =
heat in - work out
closed system first law of thermodynamics
Q-W = m(u2-u1)
for a closed system there are two options
it can expand therefore does work Q-W=change in internal
or it cannot expand therefore does no work and all energy goes into internal energy
Q = change internal energy
For ideal gas u is related to
temperature via pV = mRT
heat capacity to get change in T
Cv for closed system
Cp for open system
For steam u is
in the steam tables
need to know p T to get u
and saturated or superheated
if isothermal ideal case use
PV=nRuT
Work done =
integral of pressure with respect to volume
if no work is done
constant volume therefore Q= change in internal energy
PV=mRT if T increases and V is fixed P must increase
therefore Cv used
closed system constant pressure
W= integral of force with respect to distance
=
enthalpy =
internal energy + work against constant pressure
adiabatic process Q=
0 no heat in or out
process thermally insulated from surroundings
adiabatic process work done by system
-w=u2-u1
all energy for work must come from internal energy of the system
adiabatic compress vs expand
expand work done by system therefore internal energy must decrease
compress work done on system therefore internal energy decreases
isentropic =
entropy does not increase or decrease
