On a pv diagram, isothermal processes and isentropic processes look similar, as
ID: 1504311 • Letter: O
Question
On a pv diagram, isothermal processes and isentropic processes look similar, as shown below, but they have quite different properties. Note that both of the processes pictured are expansions, which means that each gas is doing positive work onits environment.
a) For path A (isothermal), where did the energy for that work come from? Explain.
b) For path b (isentropic), where did the energy for that work come from? Explain.
c) Since A is not isentropic, the gas entropy must have changed during the process. Did it increase or decrease and how can you tell?
d) Since B is not isothermal, the gas temperature must have changed during the process. Did it increase or decrease and how can you tell?
Explanation / Answer
for isothermal
W = nRT*ln(Vi/Vf)
Q = U + W
U = 0 because isothermal
Q = W
energy will come through the volume and pressure change
part b )
Q = 0 for isentropic
dU = -pdV
change in volume
part c )
entropy is measure of randomness
volume is increase in so randomness will increase so entropy will increase
part d )
(T2/T1) = (V1/V2)^y-1
y = diatomic gas = 1.4
T1 > T2
it will decrease