[galpinj]

Quick question about friction:

I was watching a video on Khan Academy, and he pointed out that no process can be truly reversible. In his example, a piston is moved after an infinitesimal change to the weight on the piston. In reality, this would cause some heat to be lost due to friction. My question is, why does this heat loss matter? Does the heat lost between the piston and cylinder walls come from the average kinetic energy of the molecules in the cylinder? I'm confused as to how the heat/friction associated with the piston/cylinder walls are associated with the gas in the system. I think the gas has to exert more energy to push the piston up, lowering its average KE, but I'm not sure.

Thank you for helping clarify this for me

Link: https://www.khanacademy.org/science/chemistry/thermodynamics-chemistry/internal-energy-sal/v/quasistatic-and-reversible-processes

[Borek]

I think the gas has to exert more energy to push the piston up

Yes, some of the gas energy is converted not into a piston motion (which would be a simple PΔV work) but into heat of the piston and cylinder.