# What is the physical interpretation of enthalpy and entropy?

1. Sep 1, 2007

### mune

Hi guys, I need help on thermodynamics:

1. what is the physical interpretation of enthalpy and entropy?

2. in an open system, change in total energy = change in enthalpy?

3. every reversible process must be adiabatic?

4. what does clausius inequality means?

5. Q-W=U is for closed system? and Q-W= enthalpy + KE + PE is for steady state open system?

thanks

2. Sep 2, 2007

### happygiant

clasius equality means that net entropy of an isolated system increases.

3. Sep 2, 2007

4. Sep 3, 2007

### mune

1. what is the physical interpretation of enthalpy and entropy?
enthalpy, U+PV, is the heat can be used to do work and entropy, dQ/T is a measure of randomness. but i still don't understand, what does a large change in enthalpy and a small change in enthalpy means physically? same for entropy.

2. in an open system, change in total energy = change in enthalpy?
this one i don't quite understand, i saw it in an example, wonder if it is always true.

3. every reversible process must be adiabatic?
because reversible process does not leave trace to environment, so i guess dQ=0, which is adiabatic. But I am not too sure about it.

4. what does clausius inequality means?
sum of Q/T of a cyclic process is zero, if it is reversible, and less than zero, if it is irreversible. but i don't know what is the use of this inequality, what does it implies? if it measures entropy, then why do we need to know change in entropy?

5. Q-W=U is for closed system? and Q-W= enthalpy + KE + PE is for steady state open system?
this one i knew the answer. yes and yes.

pls tell me if you know anyone of the answers. Thanks!

5. Sep 3, 2007

### kaisxuans

i have informayion on it!
come and visit my blog and you will see half a page of it!
Thermodynamics
but im not that sure if it will help
because i posted the info on differnt types of it.