# Thermal Equilibrium (Simple Question)

I'm beginning to revise the basic concepts of statistical mechanics and I came across the definition of thermal equilibrium.

'Two thermodynamic systems are in thermal equilibrium with each other if there is no net flow of thermal energy between them.'

There's also this:

'A system is said to be in thermal equilibrium with itself if the temperature within the system is spatially uniform and temporally constant.'

My question is simple: does the absence of exchange of thermal energy mean that both systems are at the same temperature?

Thermal Equilibrium Definition

• I agree with the other answers, but here's perhaps an interesting question. What would happen if two systems, one meeting the second definition of internal thermal equilibrium (call it System A with equilibrium temperature $T_A$) and another not meeting the second definition of internal thermal equilibrium (call it System B) were brought into contact with one another and isolated from everything else? Could they be in thermal equilibrium with one another per the first definition, i.e. based on there being no net transfer of heat between them? I believe they could. May 18, 2021 at 22:05

In the post, Note if there is a flow between the surrounding and $$A$$, then this means surrounding and $$A$$ are not in thermal equilibrium. Thus there would be a change in temperature unless surrounding and $$A$$ come to thermal equilibrium.
The same goes for $$A$$ and $$B$$. So the state of thermal equilibrium corresponds to $$A$$, $$B$$ and surrounding have the same temperature. That's what has been pointed out by @sam.