Entropy for Reversible and Irreversible Reactions

[SandraChane_1B]

Does the way that you calculate the change in entropy change depending on if the reaction is reversible or irreversible? If so, how does it change? How would you know if a reaction is reversible or not?

[Brian Huynh 2L]

Because entropy is a state function (the path to the final result does not matter) the method used to calculate entropy for a irreversible versus reversible does not matter. Therefore, we can use the same equation for both processes. Reversible reactions, which are not common, needs to be a system where infinitely small changes affect the system drastically. For example, in an irreversible system Pex = 1atm and Pint = 2atm it will expand but even if we decrease Pex to 0.999999atm or 1.00000001atm it will still expand. On the other hand, reversible systems Pex = 2atm and Pint = 2atm if we decrease Pex to 1.9999atm the system will expand, yet if we increase Pex to 2.000001 atm then the system will compress- the main idea is that infinitely small changes to the system yields a different outcome (expansion versus compression)

[Janelle2E]

Entropy is zero in a reversible process, and it increases in an irreversible process, such as the transfer of heat from a hot object to a cold object (entropy increases). The process to figure out the entropy for both is the same. A reversible process is one in which both the system and its environment can return to exactly the states they were in by following the reverse path. An irreversible process is one in which the system and its environment cannot return together to exactly the states that they were in.