Chapter 13, Problem 1CQ

What does it mean to say that two systems are in thermal equilibrium?

To determine

If two systems are in thermal equilibrium, what does mean of it?

Answer to Problem 1CQ

For two systems in contact, heat flows from higher temperature to lower temperature.

Explanation of Solution

If two systems are in thermal equilibrium, there must exist a common property which remains the same. This property is the temperature. For two systems in contact, heat flows from higher temperature to lower temperature and systems reach the same temperature. It means both systems have the same average kinetic energy per particle.

Temperature gives a measure of hotness or coldness of a body.

Conclusion:

For two systems in contact, heat flows from higher temperature to lower temperature.