For purposes of illustration lets assume that this is Gaussian with standard deviation 5 cm. After the explosion it is reasonable to suppose, continuing to assume a Gaussian distribution, that the standard deviation is now 10's of meters. The reason for picking the Gaussian for this ilustration is that the entropy of a Gaussian distribution varies directly as the standard deviation. We can no longer be assured that that one state is the one we would expect the system to be in.
We know less about the system. Uncertainty has gone up. Entropy has increased. The important thing to realize when confronted with this formula is that the states have to be equally probable.
In the Shannon based definition they don't. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams?
Learn more. Asked 3 years, 9 months ago. Active 3 years, 9 months ago. The description of the second law stated on this slide was taken from Halliday and Resnick's textbook, "Physics".
It begins with the definition of a new state variable called entropy. Entropy has a variety of physical interpretations, including the statistical disorder of the system, but for our purposes, let us consider entropy to be just another property of the system, like enthalpy or temperature.
The second law states that there exists a useful state variable called entropy. The change in entropy delta S is equal to the heat transfer delta Q divided by the temperature T. For a given physical process, the entropy of the system and the environment will remain a constant if the process can be reversed.
If we denote the initial and final states of the system by "i" and "f", then:. An example of a reversible process would be ideally forcing a flow through a constricted pipe. Ideal means no boundary layer losses. As the flow moves through the constriction, the pressure, temperature and velocity would change, but these variables would return to their original values downstream of the constriction.
The state of the gas would return to its original conditions and the change of entropy of the system would be zero. The second law states that if the physical process is irreversible , the entropy of the system and the environment must increase; the final entropy must be greater than the initial entropy.
An example of an irreversible process is the problem discussed in the second paragraph where a hot object is put in contact with a cold object. But if you perform an x process, and then perform a y process instead of a -x process where x ne y , then you've performed an irreversible process, which is not necessarily cyclic That is, the path apparently does matter, when it shouldn't for a state function.
If you perform an x process and then a -x process, you've performed a reversible cyclic process. Now, you CAN say this:. Why is entropy equal to q for a reversible process? What is the difference between reversible and irreversible? Chemistry Thermochemistry Entropy. Truong-Son N. May 27, Same with a liquid vs. You ideally retain all the heat that you add.
Related questions How does entropy change with pressure? How do you calculate entropy?
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