Solving Irreversible Processes: Q-W=U2-U1

AI Thread Summary
An isentropic process can be irreversible if it maintains constant entropy while increasing the universe's entropy, leading to energy loss. Desiring less irreversible processes is linked to achieving higher efficiency, as irreversible processes waste energy through entropy increase. The first law of thermodynamics applies to both reversible and irreversible processes, but energy loss occurs in irreversible processes due to entropy. Examples of isentropic irreversible processes were requested, particularly in the context of efficiency. Overall, working with reversible processes is preferred to minimize energy loss and maximize efficiency.
Dili
Messages
13
Reaction score
0
I am having trouble with these questions. Can anyone help please

1. How is it possible to have an isentropic process which is irreversible?

2.Why is it desirable to have processes which are less irreversible?

3. Is the expression for the 1st law of thermodynamics for a closed system process is same for both reversible and irreversible processes?
i.e. Q -W = U2-U1
 
Physics news on Phys.org
A reversible process does not imply that system entropy is not changing, but universe entropy not increasing. So, the process can proceed in such a way that system entropy does not change and entropy of the system environment (the univers) will increase. So such a process would be irreversible.

Desirable? Something is desirable if it helps in pursuing a target. If you are looking for a big blast, for sure it won't be reversible. If you are lloking for a rechargeable battery, you would like to design an electrochemical process that proceeds closely reversibly.

For the third point, I would say that for irreversible processes this equation does not apply. There is always some loss of energy when the process is not reversible: this is entropy.
 
Thanks vivesdn

In the 1st question can you give an example for an isentropic irreversible process?

In the second question i was referring in line with efficiency

Can you give an equation of 1st law of thermo that applies to the irreversible process?

Any replies/opinions from others are welcome as well
 
All irreversible processes have an efficiency problem: universe entropy increases, so there is some energy loss (not disappeared, just invested in increasing universe disorder). But this is the toll you have to pay if you want something to happen quickly. As the process is more reversible, the less energy lost in entropy increase. So in terms of efficiency you would like to work always with reversible processes.
 
vivesdn said:
For the third point, I would say that for irreversible processes this equation does not apply. There is always some loss of energy when the process is not reversible: this is entropy.
In physics, laws are never broken. The first law always applies between any two equilibrium states. It does not depend upon the efficiency of the process in getting from one state to the other.

AM
 
Andrew Mason said:
In physics, laws are never broken. The first law always applies between any two equilibrium states. It does not depend upon the efficiency of the process in getting from one state to the other.

AM

OK. I must agree. The irreversible process will have a lower value for W than the corresponding reversible process between the same states (characterized by U1 and U2 ).
 

Thread 'Errors and significant figures'

I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
View full post »
Thread 'Collision of a bullet on a rod-string system: query'

Thread 'Collision of a bullet on a rod-string system: query'

In this question, I have a question. I am NOT trying to solve it, but it is just a conceptual question. Consider the point on the rod, which connects the string and the rod. My question: just before and after the collision, is ANGULAR momentum CONSERVED about this point? Lets call the point which connects the string and rod as P. Why am I asking this? : it is clear from the scenario that the point of concern, which connects the string and the rod, moves in a circular path due to the string...
View full post »
Thread 'A cylinder connected to a hanging mass'

Thread 'A cylinder connected to a hanging mass'

Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
View full post »

Similar threads

Change in entropy of the surroundings in an irreversible process
Replies
14
Views
939
Thermodynamics Problem: Reversible and Irreversible Processes
Replies
1
Views
1K
Entropy change and reversible/irreversible processes
Replies
1
Views
2K
Chemistry Entropy in isolated composite system for irreversible process
Replies
3
Views
2K
I Focus Problem for Entropy Change in Irreversible Adiabatic Process
2
Replies
60
Views
9K
Chemistry A few questions on an irreversible adiabatic expansion of an ideal gas
Replies
1
Views
2K
Chemistry For irreversible process from state 1 to 2, why can the system not be isolated for reversible process from 1 to 2?
Replies
2
Views
2K
B Entropy change for reversible and irreversible processes
Replies
12
Views
2K
How to calculate the entropy for two sources
Replies
5
Views
1K
I Irreversible Isochoric Process in a Cycle
Replies
8
Views
3K

Hot Threads

Recent Insights

Back
Top