Irreversible process andReversible processRelativity refers to a process in which the reverse process cannot repeat every state of the positive process without causing other changes.Common irreversible processes are: non isothermal transfer;Throttling process；Free expansion；blendProcess.
Chinese name
Irreversible process
Foreign name
Irreversible process
Nature
Any actual process is irreversible
Features
Will not spontaneously reverse
Common processes
Non isothermal transfer;Throttling process, etc
Definition
Under the condition of not causing other changes, the reverse process cannot repeat the process of each state of the positive process
The change process of nature is irreversible.The so-called irreversibility refers to thosespontaneousIt is impossible to spontaneously return to the originalstateWithout any impact on the outside world.[1]
In physics, the definition of reversible and irreversible processes is: a system starts from a certain state and reaches another state through a certain process. If there is another process, it can completely restore the system and the outside world (the system returns to the original state and eliminates all the influences of the system on the outside world), then the original process is called a reversible process;On the contrary, if it is impossible to completely recover the system and the outside world by any means, the original process is called irreversible process.The river can flow from high to low, which is an irreversible process, because water can not spontaneously return from low to high again.The word "spontaneously" is very important here, because we can use a pump to pump water from the low to the high, that is, we need the outside world to do work on the water, so the outside world has changed and had an impact, which is impossible to eliminate.Such examples can be cited in many ways: coal combustion can give off heat, and conversely, it is impossible to completely recover the heat released and then turn it back into coal;The gestation, growth, aging and death of life cannot be reversed.
Is there a reversible process?It should be said that it only exists in theory, only the ideal non dissipativeQuasi-static processIt is reversible.The conditions here are ① non dissipative process, ② quasi-static process.
All irreversible processes are carried out in the direction of entropy increase, that is, towards the "depreciation" of energy.[1]
characteristic
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Irreversible processes have the following characteristics[1]：
(1) All spontaneous processes in nature are irreversible processes;
（2）out-off-balanceanddissipationThe existence of other factors is the cause of the irreversible process. The process is reversible only when the system is infinitely close to the equilibrium state at each step of the process, and there are no dissipation factors such as friction;
(3) Irreversible process is not a process that cannot be carried out in the opposite direction, but when the reverse process is completed, the impact on the outside world cannot be eliminated.
Example 1
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Take a hard blown balloon into the room and open its air vent.The compressed high-pressure gas in the balloon will flow out.In the future, all marbles will be evenly distributed in the room.If you have to wait for these marbles to automatically return to the balloon again, it will be a waste of time.The uniform distribution of air will become a long-term and lasting equilibrium distribution.
Example 2
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Experiment 9-1: Can you recover ice?
Pour a piece of ice into a glass of warm water and wait.What will happen?The ice will melt away.Can the melted ice still gather together and jump out of the glass in the shape of the original ice?(Of course you can imagine such a thing, but don't expect it to happen.)
What makes us realize that this process cannot be reversed?Let's film this process.Turn the movie upside down.If you think the movie released in this way is absurd and abnormal, the process is irreversible.
All processes occurring in a closed system are irreversible to time.The conclusion of this empirical fact is the same as what the second law tells us: in a closed system composed of many components, there is always an unordered distribution behind the ordered distribution, not the reverse.
Example 3
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Experiment 9-2: Is the swing of the pendulum reversible?
Hang an object on a line several inches long and make it swing slightly.Observe the change of swing amplitude.If we only observe the swing once or twice, we may think that it is a reversible process, and its kinetic energy and potential energy are
And remain constant.But the swing amplitude and swing height began to decrease slowly.Finally, the object is stationary at its lowest position.Its energy decreases continuously in the swing process, and its final state energy is the minimum value: 0.
