How are heat and entropy different?

tsimionescu · 2024-07-22T08:29:39 1721636979

Heat is energy that causes something to raise in temperature, and is measured in Joules. Entropy is a harder to pin down concept, related to the internal state of a system, and is measured in Joules/kelvin. In certain processes, the change in entropy is equal to the change in heat divided by the temperature of the system.

ainoobler · 2024-07-22T08:47:35 1721638055

Sounds like it's the same thing.

HPsquared · 2024-07-22T09:09:04 1721639344

They are closely related but not the same. DeltaS = DeltaQ /T

A lot of it comes down to whether a process is reversible or not. I've taken multiple courses on thermodynamics and still only understand it a little.

tsimionescu · 2024-07-22T09:00:33 1721638833

It is not. Two bodies can have different entropy even if they are emitting the same amount of heat.

ainoobler · 2024-07-22T09:06:17 1721639177

Where are the calculations?

tsimionescu · 2024-07-22T09:14:55 1721639695

dS = dQ / T

ainoobler · 2024-07-22T16:41:16 1721666476

So T = dQ/dS. Seems like the same thing.

tsimionescu · 2024-07-22T18:35:24 1721673324

If they were the same thing, then T=1. Since there are many many bodies with T != 1, it follows that dQ is rarely equal to dS.