## Constant Pressure vs. Equilibrium system

Victoria Zheng--2F
Posts: 103
Joined: Fri Aug 09, 2019 12:17 am

### Constant Pressure vs. Equilibrium system

Hello. I don't quite understand the difference when the pressure of the system is constant and when the system is equilibrium, what does it mean by taking infinitesimal small steps to change the volume? Why are we using the derivative and integral to calculate the sum of all the small steps? Thank you.

Ariel Davydov 1C
Posts: 110
Joined: Thu Jul 11, 2019 12:16 am
Been upvoted: 1 time

### Re: Constant Pressure vs. Equilibrium system

If the pressure is constant, this simply means that it is not changing. For example, the external pressure could be constant and held at 1 atm, while the internal pressure of a system could be constant and held at 2 atm. However, because these pressures differ, this system is not at equilibrium with its surroundings. If you pull out the pins holding the piston (the one that is keeping the system closed), it would instantly shoot out due to the internal pressure being larger than the external pressure, which shows us that this is an irreversible process.

When the internal pressure matches the external pressure of a system, it is said to be at equilibrium and a reversible process. If you increase the internal pressure of the system little by little at infinitely small increments (“infinitesimally”), the volume change can be reversed by a likewise infinitesimal change in the system. The pressures b=must match one another rim order for this process to be reversible.