Spontaneous Process and Irreversibility

In summary, the conversation discusses the relationship between irreversible and spontaneous processes in an isolated system. It is stated that in an isolated system, dQ (change in heat) is always zero and Sb-Sa (change in entropy) is greater than or equal to zero. The question arises whether irreversible processes are always spontaneous, to which it is clarified that every spontaneous process is irreversible, but not all irreversible processes are spontaneous.
  • #1
Euphemia
12
0
Hi,all
My problem is following this picture!
http://mykomica.org/boards/shieiuping/physics/src/1325318780058.jpg
If the system is isolated, dQ is always zero. Sb-Sa ≥0
And it satisfies the requirement of spontaneousness in isolated systems.
So ,I do wonder if irreversible process is always spontaneous!
Am I Right?
Euphemia
 
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  • #2
Note: Your picture isn't coming across.

You have it backwards. Every spontaneous process is irreversible, but not every irreversible process is spontaneous.
 
  • #3
A process which is irreversible is the one results in energy loss in the form of heat (dissipation) due to friction ,viscosity etc.As these are involved in processes other than natural ones- eg.,rubbing a stone againast a wall in vertically upward direction- irreversible processes need not be natural or spontaneous ones.
 

Related to Spontaneous Process and Irreversibility

1. What is a spontaneous process?

A spontaneous process is a physical or chemical change that occurs without the input of external energy. It happens naturally and tends to move a system towards a state of lower energy, greater stability, or higher entropy.

2. What is the difference between a spontaneous and non-spontaneous process?

A spontaneous process occurs on its own, while a non-spontaneous process requires an input of external energy to occur. Non-spontaneous processes are also called "unfavorable" because they move a system towards a state of higher energy or lower entropy.

3. Can a spontaneous process be reversed?

In most cases, a spontaneous process is irreversible. This means that once it has occurred, it cannot be reversed without an input of external energy. This is because spontaneous processes tend to move towards a state of greater disorder and it is highly unlikely for the molecules to reorganize themselves back to their original state.

4. What is the role of entropy in spontaneous processes?

Entropy is a measure of the disorder or randomness in a system. In spontaneous processes, the overall entropy of the system tends to increase, meaning that the molecules become more disordered. This is because there are more ways for the molecules to be arranged in a disordered state compared to an ordered state.

5. Can a spontaneous process violate the laws of thermodynamics?

No, a spontaneous process follows the laws of thermodynamics. The second law states that the total entropy of an isolated system always increases or remains constant over time. A spontaneous process may seem to violate this law on a small scale, but when looking at the entire system, the overall entropy will always increase.

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