two system to change. The changes goes to until finally all measured properties of each system approach constant values. When this occurs, we say that the two systems are in thermal equilibrium with each other 2. Zeroth law of thermodynamics If system a and b are each in thermal equilibrium with a third system C, then a and b are in thermal equilibrium with each othertwo system to change. The changes goes to until finally all measured properties of each system approach constant values. When this occurs, we say that the two systems are in thermal equilibrium with each other. 2. Zeroth law of thermodynamics “If system A and B are each in thermal equilibrium with a third system C, then A and B are in thermal equilibrium with each other