[cyberax]

You are correct. Although technically, dissolution is not a reversible process. That's why you need to input energy to reverse it.

Carnot cycle, technically, doesn't apply to all energy sources directly.

For example, solar panels have their "hot side" at around 6000K, so Carnot efficiency would be close to 100%. Real solar panels have other limiting factors, and I believe the absolute achievable theoretical maximum is around 80%.

On the other side of the spectrum, wind turbines have very lousy Carnot efficiency because they're exploiting a temperature difference of just a few degrees. However, the "Carnot tax" is not paid by us directly, so we don't really care about it.