Changes in closed system

For each of these idealized models there is a stationary state. For a continuous open system, this is the steady state. Rate laws and steady material flows arc required to define the steady state. For a closed system, equilibrium is the stationary state. Equilibrium may be viewed as simply the limiting case of the stationary state when the flows from the surroundings approach zero. The simplicity of closed-system models at equilibrium is in the rather small body of information required to describe the time-invariant composition. We now turn our attention to the principles of chemical thermodynamics and the development of tools for the description of equilibrium states and energetics of chemical change in closed systems. 

Until now, we have only allowed a single parameter but it is also possible to observe two or more transformations or other types of change at the same time. Spontaneous changes in closed systems at constant T and p are only possible in the direction in which the free energy decreases, in this case, the Gibbs energy ... 

Another simple class of processes consists of temperature changes in closed systems without phase change or chemical reaction. If the pressure is constant, the relations of Eqs. (2.5-6) and (2.5-8) give... 

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