Reversible and Irreversible Processes-Free PDF
You often do not acknowledge several physical, chemical and other changes happening around you. Some of these processes cannot even be felt, with their existence often eluding you. However, these processes do occur and there is a difference in the state of the participants taking part in these processes.
For instance, boiling of water, melting of ice, burning of things, etc. All these are processes that are distinct in nature, although, in all of them, one aspect is common. There is an exchange of heat or energy in each case, and they can be classified under reversible and irreversible processes.
What is a Reversible Process?
A reversible process is the process where it never occurs; on the contrary the irreversible process is the one which can be said to be the natural process and cannot be reversed.
For example water changing into water vapor is a reversible process whereas tearing the page is an irreversible process. This is because can we tear the pages? No we cannot so the process cannot be reversed.
Thermodynamics is the example of the reversible process. Here the system and the surroundings return to the same stage at the end of the process.
Students should note that a reversible process takes two processes into account. While in the first process participants convert into another form, in the case of this second process the reverse reaction takes place where the resultants get back to the initial stage.
Hence, understanding this will help in further delving into the difference between reversible and irreversible processes. You should also note that understanding these processes is not just vital for your Physics curriculum, but also that of chemistry.
Types of Reversible Processes
There are two types of reversible processes. The internally reversible process and the external reversible process.
Internal reversible process involves no irreversibilities within the system boundaries. This states that the system undergoes the stage of equilibrium but when it returns it again passes through the sme stage.
In other words we can define a reversible process in simple words that the process that can be reversed completely.
In the externally reversible process there are no irreversibilities. For example we can say about reservoirs and the system.
What is an Irreversible Process?
To understand this, consider a reversible process example - the cooking of food. You begin by arranging the necessary ingredients - vegetables, spices and meat and cook the entire thing and prepare a dish. Now, however hard you try, you cannot get back the ingredients in their original form. Another fine example is that of fuel consumption where once converted into energy, the process cannot be reversed to get back the fuel.
They have already been turned into something new which possess a completely different set of properties. Yet another crucial aspect that comes here is that the participants lose their individual characteristics in an irreversible process.
Therefore, students should be cautious while studying both reversible processes and irreversible processes. Each process or method should be carefully analyzed so as to understand its type.
Reversible and Irreversible Process in Thermodynamics
In terms of thermodynamics, a reversible process is where the participants go back to its initial form by inculcating minor or negligible changes in their surroundings. Contrarily, an irreversible process is a naturally occurring phenomenon, which does not go back to its original state.
Students should be able to tell the difference between reversible and irreversible processes in thermodynamics only when they have built an understanding of the same.
Factors behind Irreversibility of a Process
A reversible process has certain consciousness if the procedure has to be undergone.
There should be absence of the dissipative force and the second condition is that the process should be in a small time.
On the other hand, an irreversible process can be said to be the thermodynamics process that departs equilibrium.
When we talk in terms of pressure we can say that it occurs when the pressure of the system changes and the volume does not have time to reach equilibrium.
One of the points to note is that the system and the surrounding does not come back to the original state even after the completion of the process in the spontaneous process.
The Reversible Nature of a Process is Dependent on Multiple Factors Such as -
Non-elasticity
Friction
Electrical resistance
Magnetic resistance or hysteresis
As a student, it is important you have an idea of the various criteria for reversible and irreversible processes.
To know more about what is a reversible and irreversible process, check our online learning programmes for an in-depth understanding. You will get access to high quality lessons that will help you in building these vital concepts from their grassroot level.
You can even get your learning materials on our Vedantu app where we explain reversible and irreversible processes and every other necessary concept in the most detailed manner.
FAQs on Reversible and Irreversible Processes
1. What are reversible and irreversible processes in thermodynamics? Provide a simple example for each.
A reversible process is a theoretical process that can be reversed to restore both the system and its surroundings to their exact initial states without any net change. An example is the extremely slow melting of an ice cube in water that is at 0°C. An irreversible process is a process that cannot be reversed to restore its original state and that of its surroundings. A common example is burning a piece of paper, which turns into ash and cannot be converted back to paper.
2. What are the key differences between a reversible and an irreversible process?
The main differences between reversible and irreversible processes are:
- Speed: Reversible processes occur infinitely slowly (quasi-statically), while irreversible processes happen at a finite, often rapid, speed.
- Equilibrium: A system remains in thermodynamic equilibrium at all stages of a reversible process. In an irreversible process, the system is only in equilibrium at the initial and final states, not during the transition.
- Path: A reversible process can follow the exact same path in reverse. An irreversible process cannot.
- Work Done: The work done by the system is maximum in a reversible process compared to any irreversible process between the same two states.
- Nature: Reversible processes are ideal concepts, while all natural, real-world processes are irreversible.
3. What are some common examples of irreversible changes we see in daily life?
Many everyday activities are examples of irreversible processes. These include:
- Cooking food, like baking a cake or frying an egg.
- The rusting of iron when exposed to air and moisture.
- Burning fuels like wood, petrol, or LPG.
- Mixing salt or sugar in water. While you can recover the salt by evaporation, the energy used and the overall state of the universe has changed.
- The diffusion of a perfume's scent across a room.
4. Why is a truly reversible process considered an ideal concept and not practically achievable?
A truly reversible process is considered an idealisation because it requires conditions that cannot be met in the real world. For a process to be reversible, it must be completely free from dissipative forces like friction, viscosity, and electrical resistance. These forces convert energy into heat, which is lost to the surroundings and cannot be fully recovered. Furthermore, the process must occur infinitely slowly (quasi-statically) to maintain equilibrium throughout. Since all real-world processes have some friction and occur in a finite amount of time, they are inherently irreversible.
5. How do factors like friction and heat dissipation cause a process to become irreversible?
Factors like friction and other dissipative effects are the primary cause of irreversibility. When work is done against friction (e.g., a piston moving in a cylinder), some mechanical energy is converted into thermal energy (heat). This heat dissipates into the system and its surroundings, increasing their internal energy and overall entropy. To reverse the process, this dissipated heat cannot be spontaneously collected and converted back into useful work to move the piston back. This unrecoverable energy loss makes the process irreversible.
6. What is a quasi-static process, and why is it important for understanding thermodynamics?
A quasi-static process is a thermodynamic process that happens so slowly that the system can be considered to be in internal equilibrium at every single moment. It is a theoretical construct that serves as a close approximation for a reversible process. Its importance lies in the fact that because the system is always in equilibrium, its state variables (like pressure, volume, and temperature) are well-defined at all times. This allows us to calculate changes in properties like work and heat transfer accurately for theoretical models.
7. In thermodynamics, what makes the free expansion of a gas an irreversible process?
The free expansion of a gas (e.g., a gas in a container expanding into an adjacent vacuum) is a classic example of an irreversible process. Although no work is done (W=0) and no heat is exchanged (Q=0) during the expansion, it is irreversible for two main reasons:
- Lack of Equilibrium: The expansion is rapid and spontaneous. The system is not in equilibrium at any point between its initial and final states.
- External Work for Reversal: To reverse the process and compress the gas back to its original volume, external work must be done on the system. This act of compression will change the internal energy of the gas and/or release heat into the surroundings, leaving a permanent change. The universe is not restored to its original state, thus defining it as irreversible.
